javascript - in JS, are (a===b===c) and ( (a===b)&&(a===c)&&(b===c) ) the same? sorry for my ign

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My aim is "to execute the code when only a, b, and c are equal". I figured out two codes:

Code#1:

if (a===b===c) {console.log('something')};

code#2:

if ( (a===b)&&(a===c)&&(b===c) ) {console.log('something')};

I have tried both and realized that only "code#2" is able to respond my purpose (execute only when 3 variables are equivalent (eg. a=b=c), But for "code#1", it executes whenever there are 2 equivalent variables (eg. a=b or b=c ..)

MY QUESTION IS: "what is the difference between code#1 and code#2?"

My aim is "to execute the code when only a, b, and c are equal". I figured out two codes:

Code#1:

if (a===b===c) {console.log('something')};

code#2:

if ( (a===b)&&(a===c)&&(b===c) ) {console.log('something')};

I have tried both and realized that only "code#2" is able to respond my purpose (execute only when 3 variables are equivalent (eg. a=b=c), But for "code#1", it executes whenever there are 2 equivalent variables (eg. a=b or b=c ..)

MY QUESTION IS: "what is the difference between code#1 and code#2?"

• javascript

Share Improve this question Follow edited Feb 16, 2015 at 15:24 Sithideth Bouasavanh asked Feb 16, 2015 at 14:27 Sithideth BouasavanhSithideth Bouasavanh 1,06111 gold badge1212 silver badges2121 bronze badges 8

• 6 What's with the c flag? – Tim Čas Commented Feb 16, 2015 at 14:28
• 14 I'm pretty sure this doesn't mean what you think it means. look up the difference between "=" and "==". Then, in Javascript, "===" will bee important. – Almo Commented Feb 16, 2015 at 14:28
• 3 code #2 has a redundant parison: just check if a == b && b == c is enough – Fabrizio Calderan Commented Feb 16, 2015 at 14:33
• 2 @Almo: And even for a==b==c, that still won't mean what he (probably) thinks it means. – Tim Čas Commented Feb 16, 2015 at 14:34
• 2 I'm voting to close this question as off-topic because the author doesn't understand what he's asking. The only "correct" answer answers the actual question, but not what I think is the intent of the question. – Almo Commented Feb 16, 2015 at 14:36

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3 Answers 3

Sorted by: Reset to default 8

The question you're actually asking is whether these two are the same:

if (a === b === c) {...}
if ((a === b) && (b === c) && (a === c)) {...}

Shortly, they're not. The first can be summarized as:

if ((a === b) === c) {...}

Which, if a and b are equal, evaluates to

if (true === c) {...}

Which is not the same as checking if all three are equal.
To check three-ways equality, you will have to manually check all sides:

if ((a === b) && (b === c)) {...}  

I will try to explain the difference. Explain of first code example:

if (a=b=c) {console.log('something')};
// Code above means: if (c) {console.log('something')};
// So if Boolean(c) is false, console.log will not work

Explain of second example:

if ( (a=b)&&(a=c)&&(b=c) ) {console.log('something')};
// Code above means: if (b && c && c) {console.log('something')};
// So if Boolean(c) or Boolean(b) is false, console.log will not work

An assignment operator assigns a value to its left operand based on the value of its right operand and return the value of its right operand.

Time for a truth table... The final two columns are the expressions you're paring

A       | B     | C     | A == B    | (A == B) == C | A == B && B == C
--------+-------+-------+-----------+---------------+-----------------
TRUE    | TRUE  | TRUE  | TRUE      | TRUE          | TRUE
TRUE    | TRUE  | FALSE | TRUE      | FALSE         | FALSE
TRUE    | FALSE | TRUE  | FALSE     | FALSE         | FALSE
TRUE    | FALSE | FALSE | FALSE     | TRUE          | FALSE
FALSE   | TRUE  | TRUE  | FALSE     | FALSE         | FALSE
FALSE   | TRUE  | FALSE | FALSE     | TRUE          | FALSE
FALSE   | FALSE | TRUE  | TRUE      | TRUE          | FALSE
FALSE   | FALSE | FALSE | TRUE      | FALSE         | TRUE

Nope! They're not the same.

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