LANGUAGE » JAVASCRIPT

Variable

Last updated:
Reference:developer.mozilla.org

Types ​

Check the type of a variable, for primitive types (if used against class instances, it gives object):

js
typeof myVar;  // 'string', 'number', 'boolean', 'object', 'undefined'

Check the type of a variable, for class instances:

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myvar instanceof Date;  // true|false

Casting:

js
const flag = Boolean(0);  // !!0 - true for empty lists and objects!

Declaration ​

js
var globalVar = 'Globally or function scoped';
let localVar = 'Block scoped';
const localConst = 'Block scoped';

Global variables can be accessed through the window variable.

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window.hasOwnProperty('globalVar');
window.globalVar;