JavaScript: Parsing a bool

Question

Is there a single function (or language construct) I can use to evaluate only the following values to true (and any other values to false)?

var trueValues = [
    true,               // boolean literal
    "true",             // string literal
    "\t tRUe ",         // case-insensitive string literal with leading/trailing whitespace
    1,                  // number literal
    1.00,               // number literal
    "1",                // string literal of number literal
    "1.0",              // string literal of number literal
    "1.00000000"        // string literal of number literal
];

`!!~trueValues.indexOf(something)`. (You *did* specify "only the following values".) — , Jul 10 '12 at 17:41
Potential Duplicate: http://stackoverflow.com/questions/263965/how-can-i-convert-a-string-to-boolean-in-javascript — srini.venigalla, Jul 10 '12 at 17:41
all of the values you gave would evaluate to `true` when cast to a boolean anyways. what are you trying to accomplish? — jbabey, Jul 10 '12 at 17:42
Sounds a bit icky. You want `\t tRUe` to be `true`, but `\t tRe` to be `false`. Perhaps you should rethink your needs. — pimvdb, Jul 10 '12 at 17:47
@Engineer ECMAScript doesn't provide a mechanism for telling the difference between exact value floats and integers. — Brian Nickel, Jul 10 '12 at 18:16

Brian Nickel · Answer 1 · 2012-07-10T17:45:32.937

4

Assuming you mean those as examples and you really mean:

Interpreted as a string, contains only the case-insensitive word "true" with optional surrounding whitespace.
Interpreted as a number, evaluates to exactly 1.

The following two conditions will filter out all exceptional values.

/^\s*true\s*$/i.test(value) || Number(value) == 1

edited Jul 10 '12 at 17:45

answered Jul 10 '12 at 17:45

Brian Nickel

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Cecchi · Answer 2 · 2012-07-10T17:50:52.990

1

The following will trim any whitespace, change it to lowercase, and compare it to the string literal true. The other case that will return a true value is a number that returns 1 when passed to parseInt()

if(!String.prototype.trim) {
  bool = (val.replace(/^\s\s*/, '').replace(/\s\s*$/, '').toLowerCase() === "true" || Number(val) === 1)
} else {
  bool = (val.trim().toLowerCase() === "true" || Number(val) === 1)
}

edited Jul 10 '12 at 17:50

answered Jul 10 '12 at 17:44

Cecchi

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Good point, updated to look more like your solution except with a fallback to `.trim()`... debatable which is better but I'm liking yours for its simplicity and readability. – Cecchi Jul 10 '12 at 17:52

JavaScript: Parsing a bool

2 Answers2