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javascripttypeof

typeof usage for undefined variables

what is the best usage for the "typeof" JavaScript function?

if (typeof (myvar) == 'undefined') { 
//or
if (typeof (myvar) == undefined) { 
//or
if (typeof myvar == 'undefined') { 
//or
if (typeof myvar == undefined) {

Thanks

Solution

  • typeof is an operator, not a function, and returns a string; so do not use parentheses and do compare it to a string.

    When you compare things, avoid type coercion unless you need it (i.e. use === not ==).

    if (typeof myvar === 'undefined') {