Rewrite "if" into "switch"

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The JavaScript language
JavaScript Fundamentals
The "switch" statement

Rewrite "if" into "switch"

importance: 4

Rewrite the code below using a single switch statement:

let a = +prompt('a?', '');
if (a == 0) {
 alert( 0 );
}
if (a == 1) {
 alert( 1 );
}
if (a == 2 || a == 3) {
 alert( '2,3' );
}

The first two checks turn into two case. The third check is split into two cases:

let a = +prompt('a?', '');
switch (a) {
 case 0:
 alert( 0 );
 break;
 case 1:
 alert( 1 );
 break;
 case 2:
 case 3:
 alert( '2,3' );
 break;
}

Please note: the break at the bottom is not required. But we put it to make the code future-proof.

In the future, there is a chance that we’d want to add one more case, for example case 4. And if we forget to add a break before it, at the end of case 3, there will be an error. So that’s a kind of self-insurance.