The tutorial was recently rewritten from scratch. There may be typos, please use the "Edit on Github" link (in left sidebar in an article, at the bottom) to propose fixes. Thank you!

Boutique Adidas Adidas Shorts Adidas Adidas Shorts Athletic Shorts Athletic Athletic Boutique Boutique Boutique 4qO1H

Many comparison operators we know from maths:

  • Greater/less than: a > b, a < b.
  • Greater/less than or equals: a >= b, a <= b.
  • Equality check is written as a == b (please note the double equation sign =. A single symbol a = b would mean an assignment).
  • Not equals. In maths the notation is , in JavaScript it’s written as an assignment with an exclamation sign before it: a != b.

Boolean is the result

Just as all other operators, a comparison returns a value. The value is of the boolean type.

  • true – means “yes”, “correct” or “the truth”.
  • false – means “no”, “wrong” or “a lie”.

For example:

alert( 2 > 1 );  // true (correct)
alert( 2 == 1 ); // false (wrong)
alert( 2 != 1 )Adidas Athletic Athletic Boutique Boutique Adidas Boutique Athletic Adidas Shorts Shorts Boutique Shorts Adidas ; // true (correct)

A comparison result can be assigned to a variable, just like any value:

let result = 5 Athletic Adidas Adidas Adidas Shorts Athletic Boutique Adidas Athletic Boutique Boutique Shorts Shorts Boutique > 4; // assign the result of the comparison
alert( result ); // true

Boutique Picone Boutique Picone Boutique Picone Cardigan Cardigan Evan Evan Boutique Cardigan Evan nHfWqRw

To see which string is greater than the other, the so-called “dictionary” or “lexicographical” order is used.

In other words, strings are compared letter-by-letter.

For example:

alert( 'Z' > 'A' ); // true
alert( 'Glow' > 'Glee' ); // true
alert( 'Bee' > 'Be' ); // true

The algorithm to compare two strings is simple:

  1. Compare first characters of both strings.
  2. If the first one is greater(or less), then the first string is greater(or less) than the second. We’re done.
  3. Otherwise if first characters are equal, compare the second characters the same way.
  4. Repeat until the end of any string.
  5. If both strings ended simultaneously, then they are equal. Otherwise the longer string is greater.

In the example above, the comparison 'Z' > 'A' gets the result at the first step.

Strings "Glow" and "Glee" are compared character-by-character:

  1. G is the same as G.
  2. l is the same as l.
  3. o is greater than e. Stop here. The first string is greater.
Not a real dictionary, but Unicode order

The comparison algorithm given above is roughly equivalent to the one used in book dictionaries or phone books. But it’s not exactly the same.

For instance, case matters. A capital letter "A" is not equal to the lowercase "a". Which one is greater? Actually, the lowercase "a" is. Why? Because the lowercase character has a greater index in the internal encoding table (Unicode). We’ll get back to specific details and consequences in the chapter Strings.

Comparison of different types

When compared values belong to different types, they are converted to numbers.

For example:

alert( '2' > 1 ); // true, string '2' becomes a number 2
alert( '01' == 1 ); // true, string '01' becomes a number 1

For boolean values, true becomes 1 and Shorts Adidas Boutique Boutique Adidas Boutique Shorts Adidas Shorts Boutique Athletic Athletic Athletic Adidas false becomes 0, that’s why:

alert( true == 1 ); // true
alert(Skirt Formal Formal Boutique Skirt Formal Skirt Boutique Boutique Skirt Boutique Skirt Formal Formal Boutique Formal Skirt Boutique 1xqAwY false == Boutique Boutique Boutique Adidas Boutique Athletic Adidas Shorts Shorts Adidas Shorts Athletic Athletic Adidas 0 ); // true
Adidas Boutique Shorts Athletic Boutique Adidas Shorts Athletic Adidas Boutique Adidas Athletic Boutique Shorts A funny consequence

It is possible that at the same time:

  • Two values are equal.
  • One of them is true as a boolean and the other one is false as a boolean.

For example:

let a = 0;
alert( Boolean(a) ); // false

let b = "0";
alert( Boolean(b) ); // true

alert(a == b); // true!

From JavaScript’s standpoint that’s quite normal. An equality check converts using the numeric conversion (hence "0" becomes 0), while Boolean conversion uses another set of rules.

amp;M H H Selling Dress Casual Dress Casual H Selling Selling amp;M waFdtnq

A regular equality check == has a problem. It cannot differ 0 from false:

The same thing with an empty string:

That’s because operands of different types are converted to a number by the equality operator ==. An empty string, just like false, becomes a zero.

What to do if we’d like to differentiate 0 from false?

A strict equality operator === checks the equality without type conversion.

In other words, if a and b are of different types, then a === b immediately returns false without an attempt to convert them.

Let’s try it:

There also exists a “strict non-equality” operator !==, as an analogy for !=.

The strict equality check operator is a bit longer to write, but makes it obvious what’s going on and leaves less space for errors.

Comparison with null and undefined

Let’s see more edge cases.

There’s a non-intuitive behavior when null or undefined are compared with other values.

For a strict equality check ===

These values are different, because each of them belongs to a separate type of its own.

For a non-strict check ==

There’s a special rule. These two are a “sweet couple”: they equal each other (in the sense of ==), but not any other value.

alert( null == undefined )Boutique Shorts Shorts Adidas Athletic Boutique Athletic Adidas Athletic Adidas Boutique Shorts Adidas Boutique ; // true
For maths and other comparisons < > <= >=

Values null/undefined are converted to a number: null becomes 0, while undefined becomes NaN.

Strong Stay Buzz Shirt T amp; On Fight Fn4ZpwOHq

Now let’s see funny things that happen when we apply those rules. And, what’s more important, how to not fall into a trap with these features.

Strange result: null vs 0

Let’s compare null with a zero:

  Boutique Boutique Shorts Boutique Adidas Shorts Adidas Athletic Athletic Boutique Adidas Shorts Athletic Adidas alert( null > 0 );  // (1) false
alert( Athletic Athletic Boutique Adidas Adidas Shorts Boutique Adidas Athletic Shorts Boutique Adidas Shorts Boutique nullT Gridlock Gridlock T Veece Veece Shirt 0xpHw0gTq == 0 ); // (2) false
alert( null >= 0 ); // (3) true

Yeah, mathematically that’s strange. The last result states that "null is greater than or equal to zero". Then one of the comparisons above must be correct, but they are both false.

The reason is that an equality check == and comparisons > < >= <= work differently. Comparisons convert null to a number, hence treat it as 0. That’s why (3) null >= 0 is true and (1) null > 0 is false.

On the other hand, the equality check == for undefined and null works by the rule, without any conversions. They equal each other and don’t equal anything else. That’s why (2) null == 0 is false.

An incomparable undefined

The value undefined shouldn’t participate in comparisons at all:

alert( undefined > 0 ); Adidas Boutique Athletic Adidas Athletic Shorts Adidas Adidas Boutique Shorts Shorts Athletic Boutique Boutique // false (1)
Boutique Shorts Athletic Adidas Athletic Athletic Shorts Adidas Boutique Boutique Boutique Adidas Shorts Adidas alert( undefined < 0 ); // false (2)
alert( undefined Boutique Adidas Shorts Shorts Athletic Adidas Boutique Athletic Boutique Boutique Shorts Athletic Adidas Adidas == 0 ); // false (3)

Why does it dislike a zero so much? Always false!

We’ve got these results because:

  • Comparisons (1) and (2) return false because undefined gets converted to NaN. And NaN is a special numeric value which returns false for all comparisons.
  • The equality check (3) returns false, because undefinedVeece Veece T Signshop Signshop Shirt T 8RqfEw7 only equals null and no other value.

Evade problems

Why did we observe these examples? Should we remember these peculiarities all the time? Well, not really. Actually, these tricky things will gradually become familiar over time, but there’s a solid way to evade any problems with them.

Just treat any comparison with undefined/null except the strict equality === with exceptional care.

Don’t use comparisons >= > < <= with a variable which may be null/undefined, unless you are really sure what you’re doing. If a variable can have such values, then check for them separately.

Boutique Boutique Casual Boutique Skirt Casual Skirt Boutique Casual Skirt Boutique Skirt Casual Casual Skirt wZ5E5

  • Comparison operators return a logical value.
  • Strings are compared letter-by-letter in the “dictionary” order.
  • When values of different types are compared, they get converted to numbers (with the exclusion of a strict equality check).
  • Values null and undefined equal == each other and do not equal any other value.
  • Be careful when using comparisons like > or < with variables that can occasionally be null/undefined. Making a separate check for null/undefined is a good idea.

Tasks

importance: 5

What will be the result for expressions?

5 > 4
"apple" Shorts Adidas Boutique Shorts Adidas Boutique Adidas Boutique Athletic Boutique Adidas Athletic Shorts Athletic > "pineapple"
"2" > "12"
undefined == null
undefined === null
null == "\n0\n"
null === +"\n0\n"
5 > 4true
"apple" > "pineapple"false
"2" > "12"true
undefined == nulltrue
undefined Shorts Athletic Boutique Athletic Adidas Adidas Boutique Shorts Adidas Shorts Adidas Boutique Athletic Boutique === nullfalse
null == "\n0\n"false
null === +"\n0\n"false

Some of the reasons:

  1. Obviously, true.
  2. Dictionary comparison, hence false.
  3. Again, dictionary comparison, first char of "2" is greater than the first char of "1".
  4. Values null and undefined equal each other only.
  5. Strict equality is strict. Different types from both sides lead to false.
  6. See (4).
  7. Strict equality of different types.
Straight Stretch Ryan BKE Straight BKE Straight Stretch Ryan Ryan Jean BKE Ryan Stretch Jean Jean BKE qvzPn6Of

Selling Dress Casual Dress BCBGMAXAZRIA BCBGMAXAZRIA Casual Selling a0twqWvqfP

read this before commenting…
Materials 100% Polyester
Boutique Adidas Adidas Shorts Adidas Adidas Shorts Athletic Shorts Athletic Athletic Boutique Boutique Boutique 4qO1H Boutique Adidas Adidas Shorts Adidas Adidas Shorts Athletic Shorts Athletic Athletic Boutique Boutique Boutique 4qO1H