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Object.freeze

Make complex constant variables immutable

Mutable Object

  "use strict";
  const MATH_CONSTANTS = {
    PI: 3.14
  };
  
  MATH_CONSTANTS.PI = 99;
  
  console.log(MATH_CONSTANTS.PI);

Output:

99

Immutable Object

  "use strict";
  const MATH_CONSTANTS = {
    PI: 3.14
  };
  
  Object.feeze(MATH_CONSTANTS);
  
  MATH_CONSTANTS.PI = 99; // error
  
  console.log(MATH_CONSTANTS.PI);

Output:

TypeError: Cannot assign to read only property 'PI' of object '#<Object>'