javascript tutorial - [Solved-5 Solutions] Constants in JavaScript - javascript - java script - javascript array
Problem:
Is there a way to use constants in JavaScript?
Solution 1:
const MY_CONSTANT = "some-value";
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Solution 2:
var CONFIG = (function() {
var private = {
'MY_CONST': '1',
'ANOTHER_CONST': '2'
};
return {
get: function(name) { return private[name]; }
};
})();
alert('MY_CONST: ' + CONFIG.get('MY_CONST')); // 1
CONFIG.MY_CONST = '2';
alert('MY_CONST: ' + CONFIG.get('MY_CONST')); // 1
CONFIG.private.MY_CONST = '2'; // error
alert('MY_CONST: ' + CONFIG.get('MY_CONST')); // 1
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Solution 3:
"use strict";
var constants = Object.freeze({
"π": 3.141592653589793 ,
"e": 2.718281828459045 ,
"i": Math.sqrt(-1)
});
constants.π; // -> 3.141592653589793
constants.π = 3; // -> TypeError: Cannot assign to read only property 'π' …
constants.π; // -> 3.141592653589793
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Solution 4:
function MY_CONSTANT() {
return "some-value";
}
alert(MY_CONSTANT());
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Solution 5:
var constant = function(val) {
return function() {
return val;
}
}
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This approach gives us functions instead of regular variables, but it guarantees* that no one can alter the value once it's set.
a = constant(10);
a(); // 10
b = constant(20);
b(); // 20