(JavaScript Tutorials for Beginners)
In this end-to-end example, you will learn – JavaScript tutorials for Beginners – JavaScript Type Conversions.
JavaScript Type Conversions
In this tutorial, you will learn about type conversions in JavaScript with the help of examples.
The process of converting one data type to another data type is called type conversion. There are two types of type conversion in JavaScript.
- Implicit Conversion
- Explicit Conversion
JavaScript Implicit Conversion
In certain situations, JavaScript automatically converts one data type to another (to the right type). This is known as implicit conversion.
Example 1: Implicit Conversion to String
// numeric string used with + gives string type
let result;
result = '3' + 2;
console.log(result) // "32"
result = '3' + true;
console.log(result); // "3true"
result = '3' + undefined;
console.log(result); // "3undefined"
result = '3' + null;
console.log(result); // "3null"
Note: When a number is added to a string, JavaScript converts the number to a string before concatenation.
Example 2: Implicit Conversion to Number
// numeric string used with +, - , / , * results number type
let result;
result = '4' - '2';
console.log(result); // 2
result = '4' - 2;
console.log(result); // 2
result = '4' * 2;
console.log(result); // 8
result = '4' / 2;
console.log(result); // 2
Example 3: Non-numeric string results NaN
// non-numeric string used with +, - , / , * results to NaN
let result;
result = 'hello' - 'world';
console.log(result); // NaN
result = '4' - 'hello';
console.log(result); // NaN
Example 4: Implicit Boolean Conversion to Number
// if boolean is used, true is 1, false is 0
let result;
result = '4' - true;
console.log(result); // 3
result = 4 + true;
console.log(result); // 5
result = 4 + false;
console.log(result); // 4
Note: JavaScript considers 0 as false
and all non-zero number as true
. And, if true
is converted to a number, the result is always 1.
Example 5: null Conversion to Number
// null is 0 when used with number
let result;
result = 4 + null;
console.log(result); // 4
result = 4 - null;
console.log(result); // 4
Example 6: undefined used with number, boolean or null
// Arithmetic operation of undefined with number, boolean or null gives NaN
let result;
result = 4 + undefined;
console.log(result); // NaN
result = 4 - undefined;
console.log(result); // NaN
result = true + undefined;
console.log(result); // NaN
result = null + undefined;
console.log(result); // NaN
JavaScript Explicit Conversion
You can also convert one data type to another as per your needs. The type conversion that you do manually is known as explicit type conversion.
In JavaScript, explicit type conversions are done using the built-in methods.
Here are the commonly used explicit conversions:
1. Convert to Number Explicitly
To convert numeric strings and boolean values to numbers, you can use Number()
. For example,
let result;
// string to number
result = Number('324');
console.log(result); // 324
result = Number('324e-1')
console.log(result); // 32.4
// boolean to number
result = Number(true);
console.log(result); // 1
result = Number(false);
console.log(result); // 0
In JavaScript, empty strings and null
values return 0. For example,
let result;
result = Number(null);
console.log(result); // 0
let result = Number(' ')
console.log(result); // 0
If a string is an invalid number, the result will be NaN
. For example,
let result;
result = Number('hello');
console.log(result); // NaN
result = Number(undefined);
console.log(result); // NaN
result = Number(NaN);
console.log(result); // NaN
Note: You can also generate numbers from strings using parseInt()
, parseFloat()
, unary operator +
and Math.floor()
. For example,
let result;
result = parseInt('20.01');
console.log(result); // 20
result = parseFloat('20.01');
console.log(result); // 20.01
result = +'20.01';
console.log(result); // 20.01
result = Math.floor('20.01');
console.log(result); // 20
2. Convert to String Explicitly
To convert other data types to strings, you can use either String()
or toString()
. For example,
//number to string
let result;
result = String(324);
console.log(result); // "324"
result = String(2 + 4);
console.log(result); // "6"
//other data types to string
result = String(null);
console.log(result); // "null"
result = String(undefined);
console.log(result); // "undefined"
result = String(NaN);
console.log(result); // "NaN"
result = String(true);
console.log(result); // "true"
result = String(false);
console.log(result); // "false"
// using toString()
result = (324).toString();
console.log(result); // "324"
result = true.toString();
console.log(result); // "true"
3. Convert to Boolean Explicitly
To convert other data types to a boolean, you can use Boolean().
In JavaScript, undefined
, null
, 0
, NaN
, ''
converts to false
. For example,
let result;
result = Boolean('');
console.log(result); // false
result = Boolean(0);
console.log(result); // false
result = Boolean(undefined);
console.log(result); // false
result = Boolean(null);
console.log(result); // false
result = Boolean(NaN);
console.log(result); // false
All other values give true
. For example,
result = Boolean(324);
console.log(result); // true
result = Boolean('hello');
console.log(result); // true
result = Boolean(' ');
console.log(result); // true
JavaScript Type Conversion Table
The table shows the conversion of different values to String, Number, and Boolean in JavaScript.
Value | String Conversion | Number Conversion | Boolean Conversion |
1 | “1” | 1 | true |
0 | “0” | 0 | false |
“1” | “1” | 1 | true |
“0” | “0” | 0 | true |
“ten” | “ten” | NaN |
true |
true |
“true” | 1 | true |
false |
“false” | 0 | false |
null |
“null” | 0 | false |
undefined |
“undefined” | NaN |
false |
” | “” | 0 | false |
‘ ‘ | ” “ | 0 | true |
You will learn about the conversion of objects and arrays to other data types in the later tutorials.
Disclaimer: The information and code presented within this recipe/tutorial is only for educational and coaching purposes for beginners and developers. Anyone can practice and apply the recipe/tutorial presented here, but the reader is taking full responsibility for his/her actions. The author (content curator) of this recipe (code / program) has made every effort to ensure the accuracy of the information was correct at time of publication. The author (content curator) does not assume and hereby disclaims any liability to any party for any loss, damage, or disruption caused by errors or omissions, whether such errors or omissions result from accident, negligence, or any other cause. The information presented here could also be found in public knowledge domains.
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