## JavaScript Tutorial

Most of the time, operators and functions automatically convert a value to the correct type. That’s called “type conversion”.For example, alert automatically converts any value to a string to show it. Mathematical operations convert values to numbers.There are also cases when user need to explicitly convert a value to put things right.String Conversion in JavascriptString conversion happens when we need the string form of a value.For example, alert(value) does it to show the value. The conversion here is done automatically. We can also use a call String(value) function for that conversion manually.let value = true; alert(typeof value); // boolean value = String(value); // now value is a string "true" alert(typeof value); // stringString conversion is mostly obvious. A true becomes "true", 0 becomes "0".Number ConversionNumeric conversion happens in mathematical functions and expressions automatically.For example, when division / is applied to non-numbers, which can be converted:console.log("12"/"2"); //6 – Both strings are converted to NumberWe can use a Number(value) function to explicitly convert a value to Number. Like below:let str = "123"; let num = Number(str); console.log(typeof str); //string console.log(typeof num); //numberIf the string to be converted is not a valid number, the result of such conversion is NaN, for example:let str = "One two three"; let num = Number(str); console.log(num); //NaNSome other numeric conversion rules for explicit conversation are below//undefined becomes null let str; let num = Number(str); console.log(str); //undefined console.log(num); //NaN //null becomes 0 let str = null; let num = Number(str); console.log(str); //null console.log(num); //0 //true/false becomes 1/0 let str1 = true; let str2 = false; let num1 = Number(str1); let num2 = Number(str2); console.log(str1); //true console.log(num1); //1 console.log(str2); //false console.log(num2); //0 //In strings whitespaces from the start and the end are removed. Then, if //the remaining string is empty, the result is 0. Otherwise, the number is //“read” from the string. An error gives NaN if the string cannot be //converted. let str1 = "       "; let str2 = "  123 "; let str3 = "  123z "; let num1 = Number(str1); let num2 = Number(str2); let num3 = Number(str3); console.log(num1); //0 console.log(num2); //123 console.log(num3); //NaNProblem with addition operator(+)All mathematical operations convert values to numbers but not the addition(+) operator. In JavaScript it is used for string concatenation also. So, if one of the added values is a string then the other one is also converted to a string. Then it concatenates them:console.log(1 + "2"); //12 //1 gets converted to string and so "1" + "2" becomes "12" console.log(4 + 5 + "3");  //93 //First 4 + 5 gives 9. Since "3" is string, so 9 is converted to "9" and //the result becomes "93" console.log("3" + 5 + 4);  //354 //As with above cases "3" + 5 gives "35" and then "35" + 4 gives "354"Boolean ConversionBoolean conversion is very simple.  It follows two basic rules.Values that are “empty”, like 0, an empty string, null, undefined and NaN become false.Other values become true.console.log(Boolean(0)); //false console.log(Boolean(1)); //true console.log(Boolean("0")); //true – since non-empty string console.log(Boolean("")); //false console.log(Boolean(undefined)); //false console.log(Boolean(null)); //false console.log(Boolean(NaN)); //false

# Type Conversions in Javascript

Most of the time, operators and functions automatically convert a value to the correct type. That’s called “type conversion”.

For example, alert automatically converts any value to a string to show it. Mathematical operations convert values to numbers.

There are also cases when user need to explicitly convert a value to put things right.

## String Conversion in Javascript

String conversion happens when we need the string form of a value.

For example, alert(value) does it to show the value. The conversion here is done automatically. We can also use a call String(value) function for that conversion manually.

let value = true;
value = String(value); // now value is a string "true"
alert(typeof value); // string

String conversion is mostly obvious. A true becomes "true", 0 becomes "0".

## Number Conversion

Numeric conversion happens in mathematical functions and expressions automatically.

For example, when division / is applied to non-numbers, which can be converted:

console.log("12"/"2"); //6 – Both strings are converted to Number

We can use a Number(value) function to explicitly convert a value to Number. Like below:

let str = "123";
let num = Number(str);
console.log(typeof str); //string
console.log(typeof num); //number

If the string to be converted is not a valid number, the result of such conversion is NaN, for example:

let str = "One two three";
let num = Number(str);
console.log(num); //NaN

Some other numeric conversion rules for explicit conversation are below

//undefined becomes null
let str;
let num = Number(str);
console.log(str); //undefined
console.log(num); //NaN
//null becomes 0
let str = null;
let num = Number(str);
console.log(str); //null
console.log(num); //0
//true/false becomes 1/0
let str1 = true;
let str2 = false;
let num1 = Number(str1);
let num2 = Number(str2);
console.log(str1); //true
console.log(num1); //1
console.log(str2); //false
console.log(num2); //0
//In strings whitespaces from the start and the end are removed. Then, if //the remaining string is empty, the result is 0. Otherwise, the number is //“read” from the string. An error gives NaN if the string cannot be //converted.

let str1 = "       ";
let str2 = "  123 ";
let str3 = "  123z ";
let num1 = Number(str1);
let num2 = Number(str2);
let num3 = Number(str3);
console.log(num1); //0
console.log(num2); //123
console.log(num3); //NaN

All mathematical operations convert values to numbers but not the addition(+) operator. In JavaScript it is used for string concatenation also. So, if one of the added values is a string then the other one is also converted to a string. Then it concatenates them:

console.log(1 + "2"); //12
//1 gets converted to string and so "1" + "2" becomes "12"
console.log(4 + 5 + "3");  //93
//First 4 + 5 gives 9. Since "3" is string, so 9 is converted to "9" and //the result becomes "93"
console.log("3" + 5 + 4);  //354
//As with above cases "3" + 5 gives "35" and then "35" + 4 gives "354"

## Boolean Conversion

Boolean conversion is very simple.  It follows two basic rules.

• Values that are “empty”, like 0, an empty string, null, undefined and NaN become false.
• Other values become true.
console.log(Boolean(0)); //false
console.log(Boolean(1)); //true
console.log(Boolean("0")); //true – since non-empty string
console.log(Boolean("")); //false
console.log(Boolean(undefined)); //false
console.log(Boolean(null)); //false
console.log(Boolean(NaN)); //false #### Janani

I have learned many things from this article. It is beneficial for me. Thank you! #### Nilesh Chakrabarty

Nice example for beginners.. I m a beginner so this is very helpful for me ... so plz give this type of beginners example.. #### michael

This is a great introduction to variables in JavaScript! As a beginner to JavaScript, I found this guide very helpful in understanding the basics of variables and how they are used in JavaScript. #### qtsinfo it

Thanks for sharing the information, it is very helpful, I hope to get more such beautiful blogs from you. #### knowledge-wisdom

You have shared great information with me i appreciate your work!

## Node JS Tutorial

Build various types of web applications,command-line application,etc.
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Node JS Tutorial

Build various types of web applications,command-line application,etc....