Understanding
Type Conversion in JavaScript

What is Type Conversion?

In JavaScript, type conversion refers to changing a value from one data type to another. It is an essential concept because JavaScript is a dynamically typed language, meaning you don't need to specify data types explicitly.

There are two types of type conversions:

• Implicit Conversion (Type Coercion) - Done automatically by JavaScript.
• Explicit Conversion - Done manually in code using conversion functions.

Implicit Type Conversion (Type Coercion)

JavaScript automatically converts data types when needed. This is called type coercion.

Example 1: String and Number Concatenation

let result = '10' + 5;
console.log(result);
    

105
    

Explanation: The number 5 is implicitly converted to a string, and the result is string concatenation: '10' + '5' = '105'.

Example 2: Subtracting a String from a Number

let difference = '10' - 2;
console.log(difference);
    

8
    

Explanation: Here, JavaScript converts the string '10' to the number 10 and then performs subtraction.

Q: Why does addition with a string lead to concatenation, while subtraction leads to numerical operation?

A: JavaScript treats + as both a concatenation and arithmetic operator. If either operand is a string, it prefers string concatenation. For other operators like -, *, /, it defaults to numeric operations.

Explicit Type Conversion

Explicit conversion is when you manually convert a value using JavaScript functions like Number(), String(), or Boolean().

Example 3: Convert String to Number

let str = "42";
let num = Number(str);
console.log(num);
console.log(typeof num);
    

42
number
    

Explanation: The Number() function converts the string "42" to a number.

Example 4: Convert Number to String

let val = 100;
let strVal = String(val);
console.log(strVal);
console.log(typeof strVal);
    

100
string
    

Explanation: The String() function converts the number 100 to a string.

Example 5: Convert Values to Boolean

console.log(Boolean(0));         // false
console.log(Boolean(1));         // true
console.log(Boolean(""));        // false
console.log(Boolean("hello"));   // true
console.log(Boolean(null));      // false
console.log(Boolean(undefined)); // false
    

Explanation: Boolean() converts values to either true or false based on their "truthiness".

Truthy and Falsy Values

When converting to Boolean, JavaScript considers the following values as falsy:

• false
• 0
• "" (empty string)
• null
• undefined
• NaN

All other values are truthy.

Quick Summary

• JavaScript automatically performs implicit conversion when needed (e.g., '5' + 1 becomes '51').
• Use Number(), String(), and Boolean() for explicit conversion.
• Be cautious with + operator due to its dual nature.

Practice Question

What will be the output of the following?

console.log('5' * '2');
    

Answer:

10
    

Why? Both strings are implicitly converted to numbers before performing multiplication.