js check if var has value code example

Example 1: How can I test whether a variable has a value in JavaScript?

if (typeof variable == "undefined") {...} --> return true if variable undefined

//An empty string evaluates to FALSE in JavaScript so you can just do:
if (variable) {...}

Example 2: javascript check if undefined or null or empty string

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