(window.webpackJsonp=window.webpackJsonp||[]).push([[1770],{2178:function(t,s,a){"use strict";a.r(s);var n=a(31),e=Object(n.a)({},(function(){var t=this,s=t.$createElement,a=t._self._c||s;return a("ContentSlotsDistributor",{attrs:{"slot-key":t.$parent.slotKey}},[a("h1",{attrs:{id:"performance-tips"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#performance-tips"}},[t._v("#")]),t._v(" Performance Tips")]),t._v(" "),a("p",[t._v("JavaScript, like any language, requires us to be judicious in the use of certain language features. Overuse of some features can decrease performance, while some techniques can be used to increase performance.")]),t._v(" "),a("h2",{attrs:{id:"avoid-try-catch-in-performance-critical-functions"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#avoid-try-catch-in-performance-critical-functions"}},[t._v("#")]),t._v(" Avoid try/catch in performance-critical functions")]),t._v(" "),a("p",[t._v("Some JavaScript engines (for example, the current version of Node.js and older versions of Chrome before Ignition+turbofan) don't run the optimizer on functions that contain a try/catch block.")]),t._v(" "),a("p",[t._v("If you need to handle exceptions in performance-critical code, it can be faster in some cases to keep the try/catch in a separate function. For example, this function will not be optimized by some implementations:")]),t._v(" "),a("div",{staticClass:"language-js extra-class"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("myPerformanceCriticalFunction")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("try")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// do complex calculations here")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("catch")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("e"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        console"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("log")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("e"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),a("p",[t._v("However, you can refactor to move the slow code into a separate function (that "),a("strong",[t._v("can")]),t._v(" be optimized) and call it from inside the "),a("code",[t._v("try")]),t._v(" block.")]),t._v(" "),a("div",{staticClass:"language-js extra-class"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// This function can be optimized")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("doCalculations")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// do complex calculations here")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Still not always optimized, but it's not doing much so the performance doesn't matter")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("myPerformanceCriticalFunction")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("try")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("doCalculations")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("catch")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("e"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        console"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("log")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("e"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),a("p",[t._v("Here's a jsPerf benchmark showing the difference: "),a("a",{attrs:{href:"https://jsperf.com/try-catch-deoptimization",target:"_blank",rel:"noopener noreferrer"}},[t._v("https://jsperf.com/try-catch-deoptimization"),a("OutboundLink")],1),t._v(". In the current version of most browsers, there shouldn't be much difference if any, but in less recent versions of Chrome and Firefox, or IE, the version that calls a helper function inside the try/catch is likely to be faster.")]),t._v(" "),a("p",[t._v("Note that optimizations like this should be made carefully and with actual evidence based on profiling your code. As JavaScript engines get better, it could end up hurting performance instead of helping, or making no difference at all (but complicating the code for no reason). Whether it helps, hurts, or makes no difference can depend on a lot of factors, so always measure the effects on your code. That's true of all optimizations, but especially micro-optimizations like this that depend on low-level details of the compiler/runtime.")]),t._v(" "),a("h2",{attrs:{id:"limit-dom-updates"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#limit-dom-updates"}},[t._v("#")]),t._v(" Limit DOM Updates")]),t._v(" "),a("p",[t._v("A common mistake seen in JavaScript when run in a browser environment is updating the DOM more often than necessary.")]),t._v(" "),a("p",[t._v("The issue here is that every update in the DOM interface causes the browser to re-render the screen. If an update changes the layout of an element in the page, the entire page layout needs to be re-computed, and this is very performance-heavy even in the simplest of cases. 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This method is slightly faster than modifying the container element's "),a("code",[t._v("innerHTML")]),t._v(" property (as shown below).")]),t._v(" "),a("div",{staticClass:"language-js extra-class"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" list "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" document"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("getElementById")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"list"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" fragment "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" document"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("createDocumentFragment")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("for")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5000")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" i"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("++")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    li "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" document"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("createElement")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"li"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    li"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("innerHTML "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"item "')]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    fragment"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("appendChild")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("li"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    i"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("++")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\nlist"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("appendChild")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("fragment"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("h2",{attrs:{id:"benchmarking-your-code-measuring-execution-time"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#benchmarking-your-code-measuring-execution-time"}},[t._v("#")]),t._v(" Benchmarking your code - measuring execution time")]),t._v(" "),a("p",[t._v("Most performance tips are very dependent of the current state of JS engines and are expected to be only relevant at a given time. 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Called without argument it returns an arbitrary time but called with a previously returned value as argument it returns the difference between the two executions.")]),t._v(" "),a("p",[a("a",{attrs:{href:"https://developer.mozilla.org/en-US/docs/Web/API/Console/time",target:"_blank",rel:"noopener noreferrer"}},[t._v("Console timers"),a("OutboundLink")],1),t._v(" "),a("code",[t._v('console.time("labelName")')]),t._v(" starts a timer you can use to track how long an operation takes. You give each timer a unique label name, and may have up to 10,000 timers running on a given page.  When you call "),a("code",[t._v('console.timeEnd("labelName")')]),t._v(" with the same name, the browser will finish the timer for given name and output the time in milliseconds, that elapsed since the timer was started. The strings passed to time() and timeEnd() must match otherwise the timer will not finish.")]),t._v(" "),a("p",[a("a",{attrs:{href:"https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/now",target:"_blank",rel:"noopener noreferrer"}},[t._v("Date.now"),a("OutboundLink")],1),t._v(" function "),a("code",[t._v("Date.now()")]),t._v(" returns current "),a("a",{attrs:{href:"http://www.unixtimestamp.com/",target:"_blank",rel:"noopener noreferrer"}},[t._v("Timestamp"),a("OutboundLink")],1),t._v(" in milliseconds, which is a "),a("a",{attrs:{href:"https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number",target:"_blank",rel:"noopener noreferrer"}},[t._v("Number"),a("OutboundLink")],1),t._v(" representation of time since 1 January 1970 00:00:00 UTC until now. The method now() is a static method of Date, therefore you always use it as Date.now().")]),t._v(" "),a("p",[a("strong",[t._v("Example 1")]),t._v(" using: "),a("code",[t._v("performance.now()")])]),t._v(" "),a("p",[t._v("In this example we are going to calculate the elapsed time for the execution of our function, and we are going to use the "),a("a",{attrs:{href:"https://developer.mozilla.org/en-US/docs/Web/API/Performance/now",target:"_blank",rel:"noopener noreferrer"}},[t._v("Performance.now()"),a("OutboundLink")],1),t._v(" method that returns a "),a("a",{attrs:{href:"https://developer.mozilla.org/en-US/docs/Web/API/DOMHighResTimeStamp",target:"_blank",rel:"noopener noreferrer"}},[t._v("DOMHighResTimeStamp"),a("OutboundLink")],1),t._v(", measured in milliseconds, accurate to one thousandth of a millisecond.")]),t._v(" "),a("div",{staticClass:"language-js extra-class"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{pre:!0,attrs:{class:"token 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noreferrer"}},[t._v("compatibility"),a("OutboundLink")],1),t._v(".")]),t._v(" "),a("p",[a("strong",[t._v("Example 2")]),t._v(" using: "),a("code",[t._v("Date.now()")])]),t._v(" "),a("p",[t._v("In this example we are going to calculate the elapsed time for the initialization of a big array (1 million values), and we are going to use the "),a("code",[t._v("Date.now()")]),t._v(" method")]),t._v(" "),a("div",{staticClass:"language-js extra-class"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("let")]),t._v(" t0 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" Date"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("now")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//stores current Timestamp in milliseconds since 1 January 1970 00:00:00 UTC")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("let")]),t._v(" arr "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//store empty array")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("for")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("let")]),t._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),a("span",{pre:!0,attrs:{class:"token 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"),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1e9")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" diff"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),a("span",{pre:!0,attrs:{class:"token interpolation-punctuation punctuation"}},[t._v("}")])]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v(" nanoseconds")]),a("span",{pre:!0,attrs:{class:"token template-punctuation string"}},[t._v("`")])]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// logs: Operation took 1000002325 nanoseconds")]),t._v("\n\n")])])]),a("h2",{attrs:{id:"use-a-memoizer-for-heavy-computing-functions"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#use-a-memoizer-for-heavy-computing-functions"}},[t._v("#")]),t._v(" Use a memoizer for heavy-computing functions")]),t._v(" "),a("p",[t._v("If you are building a function that may be heavy on the processor (either clientside or serverside) you may want to consider a "),a("strong",[t._v("memoizer")]),t._v(" which is a "),a("strong",[t._v("cache of previous function executions and their returned values")]),t._v(". This allows you to check if the parameters of a function were passed before. Remember, pure functions are those that given an input, return a corresponding unique output and don't cause side-effects outside their scope so, you should not add memoizers to functions that are unpredictable or depend on external resources (like AJAX calls or randomly returned values).")]),t._v(" "),a("p",[t._v("Let's say I have a recursive factorial function:")]),t._v(" "),a("div",{staticClass:"language-js extra-class"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("fact")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token parameter"}},[t._v("num")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("num "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("===")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("?")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" num "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("*")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("fact")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("num "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),a("p",[t._v("If I pass small values from 1 to 100 for example, there would be no problem, but once we start going deeper, we might blow up the call stack or make the process a bit painful for the Javascript engine we're doing this in, especially if the engine doesn't count with tail-call optimization (although Douglas Crockford says that native ES6 has tail-call optimization included).")]),t._v(" "),a("p",[t._v("We could hard code our own dictionary from 1 to god-knows-what number with their corresponding factorials but, I'm not sure if I advise that! Let's create a memoizer, shall we?")]),t._v(" "),a("div",{staticClass:"language-js extra-class"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" fact "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("var")]),t._v(" cache "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token 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"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// End of factorial function")]),t._v("\n\n  "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("/* We return the function that checks, not the one\n  || that computes because  it happens to be recursive,\n  || if it weren't you could avoid creating an extra\n  || function in this self-invoking closure function.\n  */")]),t._v("\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" checkCache"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" \n"),a("span",{pre:!0,attrs:{class:"token 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This is a problem? Not quite, we can do some nice tricks like using JSON.stringify() on the arguments array or even a list of values that the function will depend on (for object-oriented approaches). This is done to generate a unique key with all the arguments and dependencies included.")]),t._v(" "),a("p",[t._v('We can also create a function that "memoizes" other functions, using the same scope concept as before (returning a new function that uses the original and has access to the cache object):')]),t._v(" "),a("p",[t._v("WARNING: ES6 syntax, if you don't like it, replace ... with nothing and use the "),a("code",[t._v("var args = Array.prototype.slice.call(null, arguments);")]),t._v(" trick; replace const and let with var, and the other things you already know.")]),t._v(" "),a("div",{staticClass:"language-js extra-class"},[a("pre",{pre:!0,attrs:{class:"language-js"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("function")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("memoize")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token 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If the variable is an indexed value in an array, or an attribute in an associative array, it will first look for the parent array before it finds the contents.")]),t._v(" "),a("p",[t._v("This has implications when working with performance-critical code. 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As you probably know, all numbers in JavaScript are IEEE754 double precision floating point numbers, there's no specific available representation for integers. But engines, when they can predict you only use integers, can use a more compact and faster to use representation, for example, short integers.")]),t._v(" "),a("p",[t._v("This kind of optimization is especially important for computation or data intensive applications.")]),t._v(" "),a("h4",{attrs:{id:"remarks"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#remarks"}},[t._v("#")]),t._v(" Remarks")]),t._v(" "),a("p",[t._v("Remember that premature optimization is the root of all evil. Write clear, correct code first, then if you have performance problems, use a profiler to look for specific areas to improve. Don't waste time optimizing code that's not affecting the overall performance in a meaningful way.")]),t._v(" "),a("p",[t._v("Measure, measure, measure. Performance can often be counterintuitive, and changes over time. 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