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Daniel Krupnyi
Daniel Krupnyi

Posted on • Edited on

JavaScript Basic Type Conversions Cheat Sheet 🔥

#webdev #javascript #beginners #cheatsheet

Table Of Contents

Type conversion can be explicit or implicit.

value = Number('23') // explicit
value = 5 + '25' // implicit
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Value type checking

console.log(typeof value);
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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' */
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Boolean to string 

value = String(true); /* => 'true' */
value = String(false); /* => 'false' */
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Array to string 

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

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

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

value = true + 5; /* => 6 */
value = false + 5; /* => 5 */
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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.
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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
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Undefined to boolean 

value = Boolean(undefined); /* => false */
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Null to boolean 

value = Boolean(null); /* => false */
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Object to boolean 

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

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

value = Number(true); /* => 1 */
value = Number(false); /* => 0 */
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Null to number 

value = Number(null); /* => 0 */
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Array to number 

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

Converts to zero for mathematical operations:

value = null + 5; /* => 5 */
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Undefined type conversion

Converts to NaN for mathematical operations:

value = false + undefined; /* => NaN */
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Thank's for reading! ❤️
You can also check out my redux basics cheat sheet

Top comments (6)

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geminii profile image
Jimmy •

Excellent 👌

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Daniel Krupnyi •

Thanks! Glad you liked it!

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Pawan Pawar •

Good one!!

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danielkrupnyi profile image
Daniel Krupnyi •

Thank you! 🎉

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Franck •

Nice !

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danielkrupnyi profile image
Daniel Krupnyi •

Glad you like it!