Javascript check if string if true or false and convert to Boolean

Try JSON.parse().

"true" and "false" are actually json representations of true, false. This is how ajax parses json object as a string from server side. If on server side, we return true, false => the browser will receive it as a string "true" or "false" (json representation)

if ( $(this).val() == "true" ||  $(this).val() == "false") {
    ao[id] = JSON.parse($(this).val());
}else {
    ao[id] = $(this).val();
}

DEMO

String.prototype.bool = function() {
    return (/^true$/i).test(this);
};


if ( $(this).val() == "true" ||  $(this).val() == "false") {
    ao[id] = $(this).val().bool();
}else {
    ao[id] = $(this).val();
}

This might be slightly more elegant:

var thisval = $(this).val();

if (thisval === "true" || thisval === "false") {
    thisval = (thisval === "true");
}

('' + thisval).toLowerCase() === 'true'

May be useful if extra string and toLower is negligible - may be simple.

Its true if its explicitly set to true, (boolean or case insensitive string) and false otherwise.

 // so complete solution to get the same value if neither true nor false
const thisvalStr = ('' + thisval).toLowerCase();
a[id] = thisvalStr === 'true'? true: (thisvalStr === 'false')? false: thisval;

Can be modified to include additional values like, 1, etc as per need by using || or an array.

const TrueValuesStr = ['1', 'true']

TrueValueStr.contains(('' + thisval).toLowerCase() === 'true')

In the pleasant summer of 2022, here's how I'd do it:

const thisval = $(this).val();

ao[id] = ['true', 'false'].includes(thisval) ? JSON.parse(thisval) : thisval;

You could also go a step further and have it handle numbers too:

ao[id] = ['true', 'false'].includes(thisval) || !Number.isNaN(Number(thisval))
  ? JSON.parse(thisval)
  : thisval;

var thisval = $(this).val();

switch(thisval) { 
case 'true' : 
    ao[id] = true; 
    break; 

case 'false' : 
    ao[id] = false; 
    break; 

default: 
    ao[id] = thisval; 

}

I would create an array to hold the two possible values for when the string is true or false. Then, I would search to see if thisval is found inside that array. If it is not, the indexOf function will return -1. Afterwards, it is just a matter of going over those values and build up the cases that you want.

EDIT: I have updated the code based on the suggestion of Tibos. Thank you!

I'd prob prefer

const parseMaybeBool = val =>
  typeof val === 'string'
    ? val.toLowerCase() === 'true' || val.toLowerCase() === 'false'
      ? Boolean(val)
      : val
    : val;

or w/ types

const isBool = (val: unknown): val is boolean =>
  typeof val === 'boolean' ||
  (typeof val === 'string' &&
    (val.toLowerCase() === 'true' || val.toLowerCase() === 'false'));

const parseMaybeBool = (val: unknown) =>
  isBool(val) ? Boolean(val) : val;

You can do all of this in one line if you want to:

const getBool = value => value == "true" || value == "false" ? value == "true" : value;

getBool($(this).val());

Explanation

In JavaScript you'll probably be used to using something like

if(answer == "yes"){ ...

answer == "yes" will evaluate to true or false.

For your question, this can certainly help one part of it. If there were only "true" or "false" options it would be as simple as:

const getBool = (value) => value == "true"
getBool("true"); // true
getBool("false"); // false

We can now wrap this in a ternary operator, basic overview:

`if this` ? `then do this` : `if not, then do this`

So we check if the value is true or false, and if so use the above technique.

value == "true" || value == "false" 

If its not, we can just return the value without any modifications. So the test becomes:

value == "true" || value == "false" ? value == "true" : value;

In nodejs by using node-boolify we can use isBoolean() & Boolify()

Validation Results

var isBoolean = require('node-boolify').isBoolean;

isBoolean(true); //true
isBoolean('true'); //true
isBoolean('TRUE'); //false
isBoolean(1); //true
isBoolean(2); //false
isBoolean(false); //true
isBoolean('false'); //true
isBoolean('FALSE'); //false
isBoolean(0); //true
isBoolean(null); //false
isBoolean(undefined); //false
isBoolean(); //false
isBoolean(''); //false

Boolean Conversion Results

var Boolify = require('node-boolify').Boolify;

Boolify(true); //true
Boolify('true'); //true
Boolify('TRUE'); //null
Boolify(1); //true
Boolify(2); //null
Boolify(false); //false
Boolify('false'); //false
Boolify('FALSE'); //null
Boolify(0); //false
Boolify(null); //null
Boolify(undefined); //null
Boolify(); //null
Boolify(''); //null