Are there constants in JavaScript?
Is there a way to use constants in JavaScript?
If not, what's the common practice for specifying variables that are used as constants?
Since ES2015, JavaScript has a notion of const
:
const MY_CONSTANT = "some-value";
This will work in pretty much all browsers except IE 8, 9 and 10. Some may also need strict mode enabled.
You can use var
with conventions like ALL_CAPS to show that certain values should not be modified if you need to support older browsers or are working with legacy code:
var MY_CONSTANT = "some-value";
Are you trying to protect the variables against modification? If so, then you can use a module pattern:
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
Using this approach, the values cannot be modified. But, you have to use the get() method on CONFIG :(.
If you don't need to strictly protect the variables value, then just do as suggested and use a convention of ALL CAPS.
The const
keyword is in the ECMAScript 6 draft but it thus far only enjoys a smattering of browser support: http://kangax.github.io/compat-table/es6/. The syntax is:
const CONSTANT_NAME = 0;
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