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 😄