160

I know am not the first to ask this and as I mentioned in my title ,I am trying to convert string value boolean .

I have previously put some values into local storage,Now I want to get all the values and assign all to the some boolean variables .

app.component.ts

localStorage.setItem('CheckOutPageReload', this.btnLoginNumOne + ',' + this.btnLoginEdit);

here this.btnLoginNumOne and this.btnLoginEdit are string values ("true,false").

mirror.component.ts

if (localStorage.getItem('CheckOutPageReload')) {
      let stringToSplit = localStorage.getItem('CheckOutPageReload');
      this.pageLoadParams = stringToSplit.split(',');

      this.btnLoginNumOne = this.pageLoadParams[0]; //here I got the error as boolean value is not assignable to string
      this.btnLoginEdit = this.pageLoadParams[1]; //here I got the error as boolean value is not assignable to string
}

in this component this.btnLoginNumOne and this.btnLoginEdit are Boolean values;

I tried the solutions in stackoverflow but nothing is worked.

Can anyone help me to fix this .

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1

10 Answers 10

Reset to default
304

Method 1 :

var stringValue = "true";
var boolValue = (/true/i).test(stringValue) //returns true

Method 2 :

var stringValue = "true";
var boolValue = (stringValue =="true");   //returns true

Method 3 :

var stringValue = "true";
var boolValue = JSON.parse(stringValue);   //returns true

Method 4 :

var stringValue = "true";
var boolValue = stringValue.toLowerCase() == 'true'; //returns true

Method 5 :

var stringValue = "true";
var boolValue = getBoolean(stringValue); //returns true
function getBoolean(value){
   switch(value){
        case true:
        case "true":
        case 1:
        case "1":
        case "on":
        case "yes":
            return true;
        default: 
            return false;
    }
}

source: http://codippa.com/how-to-convert-string-to-boolean-javascript/

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9 Comments

Method 5: looks too good. You can add cases for touppercase for 'ON', 'YES', 'TRUE' to ensure upper case test.
consider using "==="
You can extend method 1's regex by other test values like (/(true|1)/i).test(myString) to check for true or 1
I think I would combine method 3 & 4. I'm not sure about method 5 with "on" or "yes" returning boolean. A boolean shouldn't really be a string like that.
Old and reliable =) I also like !!'true' (as old as JS)
|
66

I have been trying different values with JSON.parse(value) and it seems to do the work:

// true
Boolean(JSON.parse("true"));
Boolean(JSON.parse("1"));
Boolean(JSON.parse(1));
Boolean(JSON.parse(true));

// false
Boolean(JSON.parse("0")); 
Boolean(JSON.parse(0));
Boolean(JSON.parse("false"));
Boolean(JSON.parse(false));
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3 Comments

This has the potential to throw an exception if the input is not valid JSON (like on or yes for example).
I had the same concern as Monkpit, but this was the only solution that I found to work when testing my application at runtime AND when unit testing.
To expand on what @KylePittman said, even values like "True" or "FALSE" where it's not all lower-case will throw an exception. If the value is undefined, it also throws an exception.
11

In your scenario, converting a string to a boolean can be done via something like someString === 'true' (as was already answered).

However, let me try to address your main issue: dealing with the local storage.

The local storage only supports strings as values; a good way of using it would thus be to always serialise your data as a string before storing it in the storage, and reversing the process when fetching it.

A possibly decent format for serialising your data in is JSON, since it is very easy to deal with in JavaScript.

The following functions could thus be used to interact with local storage, provided that your data can be serialised into JSON.

function setItemInStorage(key, item) {
  localStorage.setItem(key, JSON.stringify(item));
}

function getItemFromStorage(key) {
  return JSON.parse(localStorage.getItem(key));
}

Your example could then be rewritten as:

setItemInStorage('CheckOutPageReload', [this.btnLoginNumOne, this.btnLoginEdit]);

And:

const pageLoadParams = getItemFromStorage('CheckOutPageReload');
if (pageLoadParams) {
  this.btnLoginNumOne = pageLoadParams[0];
  this.btnLoginEdit = pageLoadParams[1];
}
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Comments

4

Define extension: String+Extension.ts

interface String {
  toBoolean(): boolean
}

String.prototype.toBoolean = function (): boolean {
  switch (this) {
    case 'true':
    case '1':
    case 'on':
    case 'yes':
      return true
    default:
      return false
  }
}

And import in any file where you want to use it '@/path/to/String+Extension'

Edit 2023: As @Elezar commented this could be unsafe to do for various reasons, so similar cases should be considere case by case.

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5 Comments

And I would like to know why webstom doesn't show me that I don't have import defined and don't suggest me import either... or how to get automatic imports working for my typescript extensions
This looks promising, but perhaps you should cast the this value here toLower() and trim() it also first ? I like the prototype approach, for C# extension methods are akin
There are some risks with updating the prototype of built-in objects. The first is that other code could be trying to add a function with the same name to the prototype. If that's the case, whichever is loaded last will be used. This can make for some very hard to diagnose bugs, especially if the implementations are only slightly different. The second problem is that a function with this name could be added to the ECMAScript standard for String at some point. Future developers would then be very confused on why this function behaves differently in this codebase than everywhere else.
@Elezar I get you... I am mostly swift / kotlin dev so I probably was trying to replicate extensions here.. But looks like you should not do that. Its old answer so I leave it just as intresting idea for others. Would be cool if they make typescript on par with swift / kotlin to allow some high level of coding and ide support...
@Renetik I understand. But the big difference between JS prototype changes and Swift extensions is that prototype changes are global. If your app uses 4 modules and you change the string prototype in moduleA, that change is going to affect the other 3 modules, even if they have nothing to do with moduleA. Or more insidiously, moduleB imports moduleQ, which imports moduleZ, which imports module42. And this 4th-level module42 suddenly works differently because the top-level app imported prototype changes from moduleA. It can be very difficult to debug.
2

This function will convert your string to boolean

export const stringToBoolean = (str: string | null | undefined) => {
    if (!str) {
        return false
    }
    if (typeof str === "string") {
        return !["0", "false", "no", "n", "null", "undefined", "nil"].includes(str.toLowerCase().trim())
    }
    return Boolean(str)
}
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1 Comment

This will return true for any string value that's not one of the 6 listed in the array. e.g., stringToBoolean("foo") will return true
2

I think this is most accurate:

function parseBoolean(value?: string | number | boolean | null) {
    value = value?.toString().toLowerCase();
    return value === 'true' || value === '1';
}

I am not sure if its good idea to include No/Yes and Y kind of values because it could add more complexity and undesired results.

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Comments

-6

just use << !! >> operator:

const Text1 = ""
const Text2 = "there is a text"

console.log(!!Text1) // false
console.log(!!Text2) // true
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1 Comment

Aight, now what happens when you have the string "false"? It returns true.
-7

You could also try using the bang bang operator if you know its a valid boolean value in the string. for e.g.

let trueAsString = 'true';

let convertedStringToBool = !!trueAsString;

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1 Comment

this only checks if the string is not an empty string, as soon as there is a character in the string the !! wil return true. Don't use this if you want to cast a string to boolean. !!'true'; // true !!'false'; // true !!''; // false
-8

You can use that:

let s: string = "true";
let b: boolean = Boolean(s);
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2 Comments

let s: string = "false"; let b: boolean = Boolean(s); @Kevin this will lead you to b=true also. So, don't use it.
@ozgurkececioglu oh gosh! Thanks for pointing that out.
-19

Boolean("true") will do the work too

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1 Comment

Boolean('false') is true. This is not a good solution. someString === 'true' is probably the best option.

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