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8-3.js
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142 lines (129 loc) · 3.43 KB
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/*調用function時参數a可忽略不傳入*/
function getPropertyNames(o, /* optional*/ a){
if (a === undefined) a = []; //也可使用 a = a || [];
for (var property in o) a.push(property);
return a;
}
/*調用function時可使用arguments.length判斷傳入的參數量*/
function f(x, y, z){
if (arguments.length != 3) {
throw new Error("function f called with " + arguments.length +
"arguments, but it expects 3 arguments.");
}
}
/*利用arguments.length判斷最大數值*/
function max(){
var maxs = Number.NEGATIVE_INFINITY;
for (var i = 0; i < arguments.length; i++){
if (arguments[i] > maxs) maxs = arguments[i];
}
return maxs;
}
function textMax(){
var largest = max(1, 10, 100, 2, 3, 1000, 4, 5, 10000, 6);
alert(largest);
}
/*利用arguments將傳入的參數變更為null*/
function ArgChange(x){
alert(x);
arguments[0] = null;
alert(x);
}
/*利用calee*/
function testArg(){
var x = 3;
//ArgChange(x);
var factorial = function(x){
if (x <= 1) return 1;
return x * arguments.callee(x-1);
};
alert(factorial(x));
}
/*建立較容易變識參數的順序寫法，可利用陣列及物件方式搭配，可讓程式碼叫為清楚*/
function arraycopy(/* array */ from, /* index */ from_start,
/* aray */ to, /* index */ to_start,
/* integer */ length){
//code gose here
}
function easycopy(args){
arraycopy(args.from,
args.from_start || 0,
args.to,
args.to_start || 0,
args.length);
}
function TestPropertoes(){
var a = [1,2,3,4], b = [];
easycopy({from : a, to : b, length : 4});
}
/*判斷參數型別，並盡可能在編譯時期報錯誤，不要在執行時期報錯，較好除錯*/
function sum(a){
if (isArrayLike(a)){
var total = 0;
for (var i = 0; i < a.length; i++){
var element = a[i];
if (element === null) continue;
if (isFinite(element)) total += element;
else throw new Error("sum(): elements must be finite numbers");
}
return total;
}
else throw new Error("sum(): argment must be array-like");
}
function isArrayLike(o) {
if (o && // o is not null, undefined, etc.
typeof o === "object" && // o is an object
isFinite(o.length) && // o.length is a finite number
o.length >= 0 && // o.length is non-negative
o.length===Math.floor(o.length) && // o.length is an integer
o.length < 4294967296) // o.length < 2^32
return true; // Then o is array-like
else
return false; // Otherwise it is not
}
function TestSum(){
var a = [1,2,3,4,5,6,7,8,9,0];
var b = {};
var tot = 0;
try
{
tot = sum(b);
}
catch(ex)
{
alert(ex);
}
alert(tot);
}
/*將傳入的參數陣列全部判斷是否為數字並加總*/
function flexisum(a){
var total = 0;
alert(arguments.length);
for (var i = 0; i < arguments.length; i++){
var element = arguments[i], n;
if (element === null) continue;
if (isArrayLike(element))
n = flexisum.apply(this, element);
else if (typeof element === "function")
n = Number(element());
else n = Number(element);
if (isNaN(n))
throw Error("flexisum(): cant's convert" + element + "to number");
total +=n;
}
return total;
}
function TestFlexisum(){
var a = [1,2,3,4,5,6,7,8,9,0];
var b = [10,20,30,40,50,60,70,80,90,100];
var tot = 0;
try
{
tot = flexisum(a, sum(b));
}
catch(ex)
{
alert(ex);
}
alert(tot);
}