Is there a standard function to check for null, undefined, or blank variables in JavaScript?

Question

Is there a universal JavaScript function that checks that a variable has a value and ensures that it\'s not undefined or null? I\'ve got this code,

Answer 1

This is the safest check and I haven't seen it posted here exactly like that:

if (typeof value !== 'undefined' && value) {
    //deal with value'
};

It will cover cases where value was never defined, and also any of these:

• null
• undefined (value of undefined is not the same as a parameter that was never defined)
• 0
• "" (empty string)
• false
• NaN

_{Edited: Changed to strict equality (!==) because it's the norm by now ;)}