JavaScript - Truthy and Falsy Expressions

In JavaScript, Truthy expressions evaluate to boolean true value and Falsy expressions evaluate to boolean false value.

Unlike other programming languages, truthy and falsy values are not limited to boolean data types and comparisons. They can have many other forms.

Let us learn what makes an expression truthy or falsy in JavaScript.

1. Falsy Expressions

There are total 6 falsy values/expressions in JavaScript. We will use testTruthyFalsy() function to check if a given value is truthy or falsy.

testTruthyFalsy Fuctionfunction testTruthyFalsy (val) 
{ 
    return val ? console.log('truthy') : console.log('falsy'); 
} 

testTruthyFalsy Fuction
`function` `testTruthyFalsy (val)` `{` `return` `val ? console.log('truthy') : console.log('falsy');` `}`

Falsy Value/Expression Description

boolean ‘false‘

Boolean false is false.

testTruthyFalsy (false); //Prints 'falsy'

Empty string i.e. ''

Any empty string is evaluated to false.

testTruthyFalsy (''); //Prints 'falsy'

undefined

Any undefined variable is equal to false.

var my_var = undefined;
testTruthyFalsy (my_var); //Prints 'falsy'

null

Any null variable is equal to false.

var my_var = null;
testTruthyFalsy (my_var); //Prints 'falsy'

NaN

Any numerical expression with result in NaN (not a number) is equal to false.

testTruthyFalsy (NaN); //Prints 'falsy'

Number zero i.e. +0 or -0

Any numerical expression with result in zero is equal to false.

testTruthyFalsy ( 2 - 2 );    //Prints 'falsy'
testTruthyFalsy ( 0 );  //Prints 'falsy'

2. Truthy Expressions

Any expression or value, other than the above listed falsy values, is considered truthy.

testTruthyFalsy Fuctionfunction testTruthyFalsy (val) 
{ 
    return val ? console.log('truthy') : console.log('falsy'); 
} 
 
testTruthy(true);           // truthy 
testTruthy(false);          // falsy 
testTruthy(new Boolean(false));   // truthy (object is always true) 
  
testTruthy('');           // falsy 
testTruthy('Packt');        // truthy 
testTruthy(new String(''));     // true (object is always true) 
  
testTruthy(1);            // truthy 
testTruthy(-1);           // truthy 
testTruthy(NaN);          // falsy 
testTruthy(new Number(NaN));    // truthy (object is always true) 
  
testTruthy({});           // truthy (object is always true) 
  
var obj = { name: 'John' }; 
testTruthy(obj);          // truthy 
testTruthy(obj.name);         // truthy 

testTruthyFalsy Fuction
`function` `testTruthyFalsy (val)` `{` `return` `val ? console.log('truthy') : console.log('falsy');` `}` `testTruthy(true);` `// truthy` `testTruthy(false);` `// falsy` `testTruthy(new` `Boolean(false));` `// truthy (object is always true)` `testTruthy('');` `// falsy` `testTruthy('Packt');` `// truthy` `testTruthy(new` `String(''));` `// true (object is always true)` `testTruthy(1);` `// truthy` `testTruthy(-1);` `// truthy` `testTruthy(NaN);` `// falsy` `testTruthy(new` `Number(NaN));` `// truthy (object is always true)` `testTruthy({});` `// truthy (object is always true)` `var` `obj = { name:` `'John'` `};` `testTruthy(obj);` `// truthy` `testTruthy(obj.name);` `// truthy`

Happy Learning !!

Truthy and Falsy Expressions

1. Falsy Expressions

2. Truthy Expressions

Weekly Newsletter

Comments

Transpiler vs Compiler

JavaScript Variable Hoisting

About Us

Tutorial Series

Meta Links

Our Blogs

Follow On: