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javascriptscopevariable-declaration
rageandqq
rageandqq

Reputation: 2281

Is there a valid way of defining a variable within the condition statement of a conditional(if) structure?

Is there a condensed way of defining a variable within the condition of an if statement in JavaScript? For example: 

var arr = [1,2,3];
console.log(len); // output is null, since it was never declared
if ((var len = arr.length) > 0) { // len  == 3
    // logic using variable 'len ' here
}

Or is the only way around this to declare and assign the value of len before the conditional statement?

Upvotes: 0

Views: 47

Answers (2)

jasonscript
jasonscript

Reputation: 6170

Based on the comment from @VictorJohnson in the other answer, I would declare my variables like below

var arr = [1,2,3], len=arr.length;
console.log(len);             // len == 3
if (len > 0) {
    // logic using variable 'len ' here

    console.log(len); 
}

This removes the possible confusion of the if block and remains quite condensed

Upvotes: 0

Jorge Zuverza
Jorge Zuverza

Reputation: 915

If your concern is the number of lines you write, you can declare len in the same line where you declare arr such as:

var len, arr = [1,2,3];
console.log(len); 
if ((len = arr.length) > 0) { // len  == 3
    // logic using variable 'len ' here

    console.log(len); 
}

I personally avoid setting values in conditionals. Conditionals are no place to set variables. It looks like an error, it leads to errors and people that read your code will be likely to miss that a variable is being set in the conditional statement.

Good luck!

Upvotes: 2

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