I would like to know if there is a way to declare a local variable inside a sequence expression in Javascript. I want to declare the variable as a part of the sequence expression and not as a separate statement.

For example, I want to do something like this:

temp = "1", var a, ++i;

Thanks for the help guys!

Edit - I am trying to instrument Javascript (to find out potential DOM-based XSS)and the above code is just a snippet of the actual program. For example, I found a way to convert if statements to expressions using the ternary operator like:

if (a === 2) {a = 1} else {a = 3}

... is converted to a === 2 ? a = 1: a = 3; ? I wanted to know if var a = 2 can also be converted to an expression so that it can be added to a sequence expression.

As to why I am doing all this - I am replacing assignment statements in a JS program with a set of statements of my own. If I add in multiple statements in place of one single statement, it messes with the rest of the code. Therefore I am using a sequence expression to get around this.

For example, in a for loop like:

for (var i = 0; i < 2; i++) {}

I cant replace i = 0 with a bunch of semicolon separated statements. Thus I am trying to add in multiple statements with a sequence operator

I would like to know if there is a way to declare a local variable inside a sequence expression in Javascript. I want to declare the variable as a part of the sequence expression and not as a separate statement.

For example, I want to do something like this:

temp = "1", var a, ++i;

Thanks for the help guys!

Edit - I am trying to instrument Javascript (to find out potential DOM-based XSS)and the above code is just a snippet of the actual program. For example, I found a way to convert if statements to expressions using the ternary operator like:

if (a === 2) {a = 1} else {a = 3}

... is converted to a === 2 ? a = 1: a = 3; ? I wanted to know if var a = 2 can also be converted to an expression so that it can be added to a sequence expression.

As to why I am doing all this - I am replacing assignment statements in a JS program with a set of statements of my own. If I add in multiple statements in place of one single statement, it messes with the rest of the code. Therefore I am using a sequence expression to get around this.

For example, in a for loop like:

for (var i = 0; i < 2; i++) {}

I cant replace i = 0 with a bunch of semicolon separated statements. Thus I am trying to add in multiple statements with a sequence operator

• javascript

Share Improve this question Follow edited Mar 12, 2023 at 10:33 Xiddoc 3,63833 gold badges1515 silver badges4040 bronze badges asked Jun 25, 2013 at 6:07 everconfusedGuyeverconfusedGuy 2,79711 gold badge3030 silver badges4444 bronze badges 19

• 2 My question is why would you want to do this? – elclanrs Commented Jun 25, 2013 at 6:12
• 1 temp = "1", var does not make any sense... It will throw a syntax error, saying unexpected token – Sushanth -- Commented Jun 25, 2013 at 6:13
• what do mean??I dont see any purpose in your question. – user2412575 Commented Jun 25, 2013 at 6:16
• 1 @IcyFlame see my previous ment, I cant use multiple statements to replace i = 0 in for(i =0; i < 2; i++){} – everconfusedGuy Commented Jun 25, 2013 at 6:40
• 1 well, yeah.. then it is correct... but you should always declare variables before starting with the loop. Though, the declaration inside the initialisation part of the loop for(var i = 0;...;...) is allowed, I prefer to do it outside the loop. Keeps things neat in the loop and it is easier to understand the structure of the loop this way. – IcyFlame Commented Jun 25, 2013 at 6:53

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5 Answers 5

Sorted by: Reset to default 3

Indeed you must begin with the var keyword followed by declarations and a semi-column. Then you can start your sequence.

If you really don't like it or do not want to use a semi-column (for whatever reason) you can try to make anonymous functions and use arguments as local variables :

(function(temp, a, i){ i=a, i++ })("1", 1)

So in a for loop you can do something like :

for (var i=function(){ /* any statement you want */; return 0 }(); i<10; i++) { /* ... */ }

Hope that helps.

Apperently you want the statement var a = this.b to be changed into something like this:

var a = this.b;
var lhs = a;
var rhs = this.b;
if(rhs == 1){
}; 
lhs = rhs;

To achieve this, you can write a separate function:

function xy(){
    var a = this.b;
    var lhs = a;
    var rhs = this.b;
    if(rhs == 1){
    }; 
    lhs = rhs;
    return a;
}

To make this work inside of a for-loop, in a single line, you can transform it into this:

for (var lhs, rhs, a = (function(){var a = this.b; lhs = a; rhs = this.b; if(rhs == 1){} lhs = rhs; return a;}).apply(this, []); a < 10; a++)

That should basically do it. The apply method guarantees that this inside the function is the same as this outside the function.

var temp="1", a , i=0;
++i;

is a clean way to do it

I still don't feel like your question makes any sense but what is wrong with this:

var a, i = 1, temp = "1"

If doesn't make sense to increment a variable you only just declared, the value would always be 1 anyway if it where possible ( assuming a default value of 0 )

If you have to increment you could do this

var a, i = 1, temp = "1", i = i + 1

Still doesn't make a lot of sense tough...

Maybe you mean this?

var temp="1",a,i=i+1;

I think you cannot use 'var' in any other way syntactically.