javascript null or undefined ou vide code example

Example 1: null undefined javascript

Undefined  used for unintentionally missing values.

Null       used for intentionally missing values.

Example 2: javascript check if undefined or null

// simple check do the job
if (myVar) {
 // comes here either myVar is not null,
 // or myVar is not undefined,
 // or myVar is not '' (empty string).
}