JavaScript switch-case internals

Question

Consider the following code:

// Checking parities
switch(queueingSystem.Priority) {
    case 1: 
         FetchGridElements();
         break;
    case 1: 
         BindToControls(this, document.getElementsByClassName("grid-controls"));
         break;
    default:
         return false;
}

Is JavaScript internally testing value as well as type against each case, equivalent to:

queueingSystem.Priority === 1

Or

queueingSystem.Priority == 1

This is actually a good question. I think it depends from browser manufactors. — Reporter, Jun 12 '13 at 09:11
@reporter No, it's precisely specified in ECMAScript. See my answer. — Denys Séguret, Jun 12 '13 at 09:14
Duplicate: [http://stackoverflow.com/questions/11019104/javascript-switch-case-are-types-compared](http://stackoverflow.com/questions/11019104/javascript-switch-case-are-types-compared) — jtomaszk, Jun 12 '13 at 09:27

score 4 · Accepted Answer · answered Jun 12 '13 at 09:12

4

It checks the strict equality === as is demonstrated by this code :

switch (1) {
  case "1":
     console.log('ok');
     break;
  default :
     console.log('nok');
}

which logs nok.

It's defined in the ECMAScript specification :

If input is equal to clauseSelector as defined by the === operator, then

answered Jun 12 '13 at 09:12

Denys Séguret

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Thanks for the specifications link. – Annie Jun 12 '13 at 09:33

score 2 · Answer 2 · answered Jun 12 '13 at 09:11

2

Types are compared:

queueingSystem.Priority === 1

answered Jun 12 '13 at 09:11

jtomaszk

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JavaScript switch-case internals

2 Answers2