What exactly is Type Coercion in Javascript?

What exactly is type coercion in Javascript?

For example, on the use of == instead of ===?

Answers:

Answer

Type coercion means that when the operands of an operator are different types, one of them will be converted to an "equivalent" value of the other operand's type. For instance, if you do:

boolean == integer

the boolean operand will be converted to an integer: false becomes 0, true becomes 1. Then the two values are compared.

However, if you use the non-converting comparison operator ===, no such conversion occurs. When the operands are of different types, this operator returns false, and only compares the values when they're of the same type.

Answer

Let’s start with a short intro to type systems which I think will help you understand the general idea of type coercion.

The type system of a language defines rules that tell us what types of data exist in that language and how they can be combined using different operators. For example, one such rule might specify that the plus (+) operator only acts on numbers. These rules exist primarily to prevent you from shooting yourself in the foot. But what happens when the programmer breaks that rule in the program? There’s nothing preventing the programmer from typing {} + {} or “hello” + 5 in a program even if the language doesn’t think those expressions make any sense.

What ultimately happens in those situations depends on how strict the language is about its type rules.

A languages type system often holds one of two positions about you breaking its rules:

  1. Say “Hey, that’s not cool!” and immediately crash your program.
  2. Say “I can’t do anything with {} … but I can do something with numbers” and attempt to convert {} to a number.

Languages with type systems that take the first position about its rules are colloquially referred to as “strongly typed” languages. They are strict about not letting you break its rules. Those that take the second approach (such as JavaScript) are referred to as “weakly typed” or “loosely typed” languages. Sure, you can break the rules, but don’t be surprised when it converts the type of data you described in your program by force in order to comply with its rules. That behavior is known as … (drum roll) ... type coercion.

Now let's look at some examples in JavaScript. First, let's start with an expression that does not lead to type coercion.

5 + 5

Using the + operator with two numbers which is perfectly valid. The program will treat + to mean “add” and happily add the two numbers. No conversion necessary.

But what about …

[] + 5

Uh oh. In JavaScript, + can mean add two numbers or concatenate two strings. In this case, we have neither two numbers nor two strings. We only have one number and an object. According to JavaScript's type rules, this makes no logical sense. Since it’s forgiving about you breaking its rules, instead of crashing it tries to make sense of it anyway. So what does JavaScript do? Well, it knows how to concatenate strings, so it converts both [] and 5 into strings and the result is string value “5”.

What’s the deal with the comparison operators == and ===? Why are there two comparison operators?

== is not immune to JavaScript’s type conversion behavior. Expressions such as 5 == “5” will evaluate to true because JavaScript will attempt to convert one of them so that it’s comparing the same type of data.

In many cases, that’s not desirable because you probably want to know if some data you’re comparing against is of a different type so that you can decide what to do about it. That’s where the === operator comes in. When you use ===, no type conversion will take place. Therefore, the expression 5 === “5” will evaluate to false.

Answer

In Python if you try to add, say, strings and integers, you get an error:

>>> "hi" + 10
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: cannot concatenate 'str' and 'int' objects

Yet in JavaScript, you don't. The 10 gets converted to a string:

> "hi" + 10
"hi10"

"Type coercion" is just a fancy misnomer for the above. In actuality, neither language has "types" in the sense of Java or C or other languages with static type systems. How the languages treat interactions between the various non-statically-typed values is a matter of choice and convention.

Answer

let me explain type coercion with the following example

Type Coercion means Javascript automatically (on-the-fly) converts a variable from one datatype to another

Ex: 123 + "4" generally raises an error but in Javascript due to type coercion, it results in 1234 a string

if(23 == "23"){
    console.log(" this line is inside the loop and is executed ");
}

In the above code, because of type coercion - JavaScript thinks 23 (number) and "23" (string) are the same thing. this makes the condition true and prints the console.log

In the other case

if(23 === "23"){
   console.log(" this line is inside the loop and is NOT executed");
}

In === case Javascript doesn't do Type Coercion, and since 23 is a number and "23" is String and because of === these two datatypes are different and that leads to the false in condition. It does not print the console.log

In simple words

In this case = it is an assignment operator - which assigns values such as var a = 3;, etc

(below operators are for comparison)

In this case == Javascript converts/coerces the datatype to another and then compares it.

In this case === Javascript doesn't convert/coerces the datatype

In order to avoid bugs and for debugging purposes === is mostly used

Please let me know the accuracy of the above information.

Answer

a == b means javascript will evaluate a against b based on if the values can be evaluated equally. For example, false == 0 will evaluate true because 0 is also the value of Boolean false. However, false === 0 will evaluate false because strictly comparing, 0 is not the same physical value as false. Another example is false == '' So basically loose comparison vs. strict comparison, because javascript is a loosely typed language. That is to say, javascript will attempt to convert the variable based on the context of the code, and this has the effect of making things equal if they are not strictly compared. php also has this behavior.

Answer

What is coercion:

Type coercion in javascript occurs when the Javascript engine has to perform a certain operation for which it needs data to be in a certain type. When the engine encounters data in a certain type that is not applicable for the operation it then coerces the data into a certain type. This is needed because variables in javascript are dynamically typed, which means that a given variable can be assigned a value of any type.

Example:


if(1){
  // 1 gets coerced to true
}


if(4 > '3') {
  // 3 gets coerced into a number
}


44 == "44"  // true, the string 44 gets converted to a nr

Boolean coercion:

In javascript coercion, all values are converted to true except for the following values which are coerced to false:

console.log(!!"");         // false
console.log(!!0);          // false
console.log(!!null);       // false
console.log(!!undefined);  // false
console.log(!!NaN);        // false
console.log(!!false);      // false

Also notice that in the above example that the double ! operator is used. The ! mark operator coerces a value into a boolean with the opposite value. We can use this operator twice to convert any value into a boolean.

Answer
var str = 'dude';
console.log(typeof str); // "string"
console.log(!str); // false
console.log(typeof !str); // "boolean"

Example of a variable which is initially declared as a string being coerced into boolean value with the ! operator

Answer

If data type is not equal with each other then Coercion Happen. like 3 == "3" or boolen == integer

Answer

Type coercion is the process of converting value from one type to another (such as string to number, object to boolean, and so on). Any type, be it primitive or an object, is a valid subject for type coercion. To recall, primitives are: number, string, boolean, null, undefined + Symbol (added in ES6).

Type coercion can be explicit and implicit.

When a developer expresses the intention to convert between types by writing the appropriate code, like Number(value), it’s called explicit type coercion (or type casting).

Since JavaScript is a weakly-typed language, values can also be converted between different types automatically, and it is called implicit type coercion. It usually happens when you apply operators to values of different types, like 1 == null, 2/’5', null + new Date(), or it can be triggered by the surrounding context, like with if (value) {…}, where value is coerced to boolean.

here is some example for implicit type coercion:

true + false
12 / "6"
"number" + 15 + 3
15 + 3 + "number"
[1] > null
"foo" + + "bar"
'true' == true
false == 'false'
null == ''
!!"false" == !!"true"
[‘x’] == ‘x’
[] + null + 1
[1,2,3] == [1,2,3]
{}+[]+{}+[1]
!+[]+[]+![]
new Date(0) - 0
new Date(0) + 0

read more: https://www.freecodecamp.org/news/js-type-coercion-explained-27ba3d9a2839/

Answer

Type coercion is the process of converting value from one type to another (such as string to number, object to boolean, and so on). Any type, be it primitive or an object, is a valid subject for type coercion. To recall, primitives are: number, string, boolean, null, undefined + Symbol (added in ES6).

Implicit vs. explicit coercion Type coercion can be explicit and implicit.

When a developer expresses the intention to convert between types by writing the appropriate code, like Number(value), it’s called explicit type coercion (or type casting).

Since JavaScript is a weakly-typed language, values can also be converted between different types automatically, and it is called implicit type coercion. It usually happens when you apply operators to values of different types, like 1 == null, 2/’5', null + new Date(), or it can be triggered by the surrounding context, like with if (value) {…}, where value is coerced to boolean.

One operator that does not trigger implicit type coercion is ===, which is called the strict equality operator. The loose equality operator == on the other hand does both comparison and type coercion if needed.

Implicit type coercion is a double edge sword: it’s a great source of frustration and defects, but also a useful mechanism that allows us to write less code without losing the readability.

Three types of conversion The first rule to know is there are only three types of conversion in JavaScript:

  • to string
  • to boolean
  • to number

Secondly, conversion logic for primitives and objects works differently, but both primitives and objects can only be converted in those three ways.

Let’s start with primitives first.

String conversion

To explicitly convert values to a string apply the String() function. Implicit coercion is triggered by the binary + operator, when any operand is a string:

String(123) // explicit
123 + ''    // implicit

All primitive values are converted to strings naturally as you might expect:

String(123)                   // '123'
String(-12.3)                 // '-12.3'
String(null)                  // 'null'
String(undefined)             // 'undefined'
String(true)                  // 'true'
String(false)                 // 'false'

Symbol conversion is a bit tricky, because it can only be converted explicitly, but not implicitly.

String(Symbol('my symbol'))   // 'Symbol(my symbol)'
'' + Symbol('my symbol')      // TypeError is thrown

Boolean conversion

To explicitly convert a value to a boolean apply the Boolean() function. Implicit conversion happens in logical context, or is triggered by logical operators ( || && !) .

Boolean(2)          // explicit
if (2) { ... }      // implicit due to logical context
!!2                 // implicit due to logical operator
2 || 'hello'        // implicit due to logical operator

Note: Logical operators such as || and && do boolean conversions internally, but actually return the value of original operands, even if they are not boolean.

// returns number 123, instead of returning true
// 'hello' and 123 are still coerced to boolean internally to calculate the expression
let x = 'hello' && 123;   // x === 123

As soon as there are only 2 possible results of boolean conversion: true or false, it’s just easier to remember the list of falsy values.

Boolean('')           // false
Boolean(0)            // false     
Boolean(-0)           // false
Boolean(NaN)          // false
Boolean(null)         // false
Boolean(undefined)    // false
Boolean(false)        // false

Any value that is not in the list is converted to true, including object, function, Array, Date, user-defined type, and so on. Symbols are truthy values. Empty object and arrays are truthy values as well:

Boolean({})             // true
Boolean([])             // true
Boolean(Symbol())       // true
!!Symbol()              // true
Boolean(function() {})  // true

Numeric conversion

For an explicit conversion just apply the Number() function, same as you did with Boolean() and String() .

Implicit conversion is tricky, because it’s triggered in more cases:

  • comparison operators (>, <, <=,>=)

  • bitwise operators ( | & ^ ~)

  • arithmetic operators (- + * / % ). Note, that binary+ does not trigger numeric conversion, when any operand is a string.

  • unary + operator

  • loose equality operator == (incl. !=).

    Note that == does not trigger numeric conversion when both operands are strings.

    Number('123') // explicit +'123' // implicit 123 != '456' // implicit 4 > '5' // implicit 5/null // implicit true | 0 // implicit

Here is how primitive values are converted to numbers:

Number(null)                   // 0
Number(undefined)              // NaN
Number(true)                   // 1
Number(false)                  // 0
Number(" 12 ")                 // 12
Number("-12.34")               // -12.34
Number("\n")                   // 0
Number(" 12s ")                // NaN
Number(123)                    // 123

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