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JavaScript | Type Conversion

 JavaScript | Type Conversion

JavaScript is loosely typed language and most of the time operators automatically convert a value to the right type but there are also cases when we need to explicitly do type conversions.
While JavaScript provides numerous ways to convert data from one type to another but there are two most common data conversions :

  • Implicit Conversion
  • explicit conversion

  • Implicit Conversion

When JavaScript tries to operate on a "wrong" data type, it will try to convert the value to a "right" type. This is known as implicit conversion.it is call Automatic type conversion


Example 1: Implicit Conversion to String
    // numeric string used with + gives string type
    let sum;

    sum = '3' + 2;
    console.log(sum) // "32"

    sum = '3' + true;
    console.log(sum); // "3true"

    sum = '3' + undefined;
    console.log(sum); // "3undefined"

    sum = '3' + null;
    console.log(sum); // "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 = '3' - true;
    console.log(result); // 3

    result = 5 + true;
    console.log(result); // 6

    result = 3 + false;
    console.log(result); // 3

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 a 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 a 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


 Explicit Conversion

we can also convert one data type to another as per our needs. The type conversion that we do manually is known as explicit type conversion. In JavaScript, explicit type conversions are done using the built-in methods.
String(), Number(), Boolean(), and Object() functions can be used to convert data from one type to another

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('314');
console.log(result); // 314

// 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


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(212);
console.log(result);  // "212"

result = String(2 + 6);
console.log(result); // "8"

//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

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