settimeout - Confused about javascript timeout -

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• is settimeout no delay same executing function instantly? 3 answers

i have function this:

var = function () {     settimeout(function () {         alert(2);     }, 0);     alert(1); }  a(); 

the result alert 1 first, alert 2

but think, though alert(2) in settimeout, executes immediately，because delay 0

why alert(1) executed first?

settimeout has default delay cause execute after alert(1) has executed.