I have written some code and in certain places == is required and in others = is required. Can someone explain the differences or point me in the direction of the resource that can?

Example:

if($("#block").css.display == "none"){
  $("#block").css.display = "block";
}

The only thing I can come up with is that in one I’m changing and in the other I’m checking. But in both I am referring to equality.

I have written some code and in certain places == is required and in others = is required. Can someone explain the differences or point me in the direction of the resource that can?

Example:

if($("#block").css.display == "none"){
  $("#block").css.display = "block";
}

The only thing I can come up with is that in one I’m changing and in the other I’m checking. But in both I am referring to equality.

• javascript
• operators
• equality
• assignment-operator

Share Improve this question Follow edited Nov 9, 2022 at 20:34 Sebastian Simon 19.5k88 gold badges6060 silver badges8484 bronze badges asked Aug 8, 2012 at 19:18 o_Oo_O 5,7371414 gold badges5555 silver badges9494 bronze badges 8

• 2 = is assignment a = b means put b inside a. . == is unstrict equality, a==b means a is roughly equal to b . a===b is strict equality and the one you should be using – Benjamin Gruenbaum Commented Aug 8, 2012 at 19:20
• 4 Any JavaScript language guide will go into details. – Dave Newton Commented Aug 8, 2012 at 19:20
• But to be fair until I asked this I wasn't aware of ===, so now I am in need to know what's the diff so thanks for that link. – o_O Commented Aug 8, 2012 at 19:28
• 2 @RKS This page covers JavaScript expressions in general. – Pointy Commented Aug 8, 2012 at 19:29
• Related: stackoverflow.com/questions/2063480/the-3-different-equals – Jonas Wilms Commented Mar 24, 2018 at 21:22

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5 Answers 5

Sorted by: Reset to default 19

= is the assignment operator. It sets a variable (the left-hand side) to a value (the right-hand side). The result is the value on the right-hand side.

== is the comparison operator. It will only return true if both values are equivalent after coercing their types to the same type.

=== is a more strict comparison operator often called the identity operator. It will only return true if both the type and value of the operands are the same.

I would check out CodeCademy for a quick intro to JavaScript.

If you prefer to read more, MDN is a great intro as well.

For those concerned about the source of the term "identity operator" jbabey pointed out that JavaScript: The Definitive Guide seems to mention it.

= assigns a value to a variable

== checks if the two parameter are equal to each other

=== checks if the two parameters are equal to each other and if their type is the same

---

! not operator

!= checks if the two parameters are not equal to each other

!== checks if the two parameters are not equal to each other or the type is not the same

---

one more

> checks if one parameter is greater than the other

>= checks if one parameter is greater than or equal to the other

>== DOESN'T EXIST

---

etcetera...

== is used to test if the value on the left is equal to the value on the right.

= is used to assign the value on the right to the variable on the left.

In javascript you have also the ===.

= This is for set the value to the variable.

== This is for compare if the value is the same.

=== This is for compare if the value is the same and also the type is the same.

The = operator is an assignment operator. You are assigning an object to a value. The == operator is a conditional equality operation. You are confirming whether two things have equal values. There is also a === operator. This compares not only value, but also type.

Assignment Operators

Comparison Operators