## DEV Community

Daniel Krupnyy

Posted on • Updated on

# JavaScript Basic Type Conversions Cheat Sheet π₯

Type conversion can be explicit or implicit.

``````value = Number('23') // explicit
value = 5 + '25' // implicit
``````

Value type checking

``````console.log(typeof value);
``````

# String conversion

#### Number to string:

``````value = String(10); /* => '10' */
value = String(10 + 40); /* => '50' */
value = (10 + 40).toString(); /* => '50' */
value = new String(10 + 20); /* => '30' */
``````

#### Boolean to string

``````value = String(true); /* => 'true' */
value = String(false); /* => 'false' */
``````

#### Array to string

``````value = String([1, 2, 3]); /* => '1,2,3' */
value = String([ ]); /* => '' */
``````

#### Object to string

``````value = String({name: "Daniel"}); /* => [object Object] */
``````

Conversion to string occurs when any data type is concatenated with a string (implicit conversion):

``````value = 30 + ' ' + 30; /* => 30 30 */ // Space is considered a symbol.
value = 30 + '' + undefined; /* => 30undefined */
``````

Mathematical operations convert Empty String to zero:

``````value = 30 - ''; /* => 30 */
value = 30 - 'text'; /* => NaN */ // If the string is not empty, then we will get NaN - calculation error.
value = 30 - '5'; /* => 25 */ // If we write a number in a string, we will get a number type
``````

# Boolean type conversion

In mathematical operations, true is converted to one and false to zero:

``````value = true + 5; /* => 6 */
value = false + 5; /* => 5 */
``````

#### String to boolean

``````value = Boolean('hello'); /* => true */ // Any non-empty string will be considered true.
value = Boolean(' '); /* => true */
value = Boolean(''); /* => false */ // An empty string will be considered false.
``````

#### Number to boolean

``````value = Boolean(-123); /* => true */ // Any number, both positive and negative, will be considered true.
value = Boolean(123); /* => true */
value = Boolean(0); /* => false */ // Zero counts as false
``````

#### Undefined to boolean

``````value = Boolean(undefined); /* => false */
``````

#### Null to boolean

``````value = Boolean(null); /* => false */
``````

#### Object to boolean

``````value = Boolean({}); /* => true */ // An empty object is considered true.
``````

#### Array to boolean

``````value = Boolean([]); /* => true */ // An empty array is considered true.
``````

# Number type conversion

#### String to number

``````value = Number('23'); /* => 23 */
value = Number('string...lalala'); /* => NaN */
value = parseInt(' 203px'); /* => 203 */ // The parseInt function reads a number from a string and removes all characters after it, but if there are characters before the number (except for a space), then it will output NaN. Serves for whole numbers.
value = parseFloat('203.212px'); /* => 203.212 */ // Works the same as parseInt, but for fractional numbers.
``````

#### Boolean to number

``````value = Number(true); /* => 1 */
value = Number(false); /* => 0 */
``````

#### Null to number

``````value = Number(null); /* => 0 */
``````

#### Array to number

``````value = Number([1, 2, 3]); /* => NaN */ // NaN refers to numbers.
``````

# Null type conversion

Converts to zero for mathematical operations:

``````value = null + 5; /* => 5 */
``````

# Undefined type conversion

Converts to NaN for mathematical operations:

``````value = false + undefined; /* => NaN */
``````

You can also check out my redux basics cheat sheet

Franck

Nice !

Daniel Krupnyy

Jimmy

Excellent π

Daniel Krupnyy