Coding Cloud

Check if variable has been declared

JS
S
JavaScript

f you are interested in knowing whether the variable hasn't been declared or has the value undefined, then use the typeof operator. 

1
2if (typeof arg !== 'undefined') {
3    // is declared || values is not undefined
4}
5
6/* Falsy Values
7false
80
9""
10NaN
11null
12undefined
13*/

Created on 3/6/2018