Why switch and if statement in Javascript treat boolean different, confused -

i've got switch , if problem in javascript, code following.

var a=0;  if(a){     console.log("a true"); } else if(!a) {     console.log("a false"); } else {     console.log("a not true or false"); }   switch(a){     case true:         console.log("switch... true");         break;     case false:         console.log("switch... false");         break;     default:         console.log("switch... not true or false"); } 

when ran code above, got result in console confused me lot:

a false switch... not true or false 

i think should this:

a false switch... false 

anyone knows why happens? appreciate answers.

if (!0) evalutes true. there rule non 0 in if evaluate true vie versa.

but switch 0 explicitly checked against case values , 0 neither true or false , hence default statement gets executed.