Coercion in JavaScript

#javascript #beginners #todayilearned #codenewbie

What is Coercion?

Coercion is the process of conversion of one data type to another.

1 + '2'
// 1 coerces to '1'
// '12'

1 + true
// true coerces to 1
// 2

1 + null
// null coerces to 0
// 1

1 + undefined
// undefined coerces to 0
// 1

'abc' + undefined
// undefined coerces to 'undefined'
// 'abcundefined'

1 < 2 < 3
// => true < 3 (left to right associativity)
// => 1 < 3 (coercion)
// => true

1 > 2 > 3
// => false > 3
// => 1 > 3
// => false

JavaScript can give weird and unexpected results when comparing. Thus, it is better to use === instead of == for comparisons as === doesn't coerce.

1 == '1'
// true
// coercion

1 === '1'
// false

Coercion decisions are made by the JavaScript Engine itself.

Manual Coercion

Here's how you can manually convert to a datatype:

const number = 42;
const string = '42';

Number(string);
// Coerces to number
// 42

String(number);
// Coerces to string
// '42'

Boolean(string);
// Coerces to boolean
// 1

Conditional Statements

The conditions inside if, ternary operator, while loop etc. are coerced to Boolean.

Truthy and Falsy

Any value that coerces to true is called truthy and to false is called falsy.

There are only 6 falsy values, everything else is truthy:

false
0
'', "" (Empty String)
null
undefined
NaN

Watch out for these:

Boolean({});
// true

Boolean([]);
//true

Boolean("0");
// true

null == 0
// false

And that's all folks! Thank-you for reading and have a wonderful day 😄

Top comments (5)

Edison Augusthy • Aug 26 '19

simplest way to convert a string to a number just add + in front of the string eg: +"3"

Sahil Bondre • Aug 26 '19

Yea, "+" followed by any data type coerces it into Number data type. Also, using "-" followed by the data type coerces it to the negative of the Number. Point to note is that this does'nt work with other operators like *, /, %.

Thank you for letting me know about this feature! Learnt something new today 😄.