I have a for loop in JavaScript that I have run through JSLint a few times. In the past I received the unexpected++ error, I decided to refactor to make my code more readable. A month or so later JSLint came out with an update and is now showing the warning...

Unexpected expression 'i' in statement position. for (i; i < scope.formData.tabs.length; i = i + 1) {

//See JSLint for why I pulled out i initialization and i = i+1 instead of i++
//and 
var i = 0;
for (i; i < scope.formData.tabs.length; i += 1) {
    scope.formData.tabs[i].show = false; // hide all the other tabs 

    if (scope.formData.tabs[i].title === title) {
        scope.formData.tabs[i].show = true; // show the new tab 
    }
}

Reverting to var i = 0 and i++ does not get improve the warnings, JSLint just stops processing.

I have a for loop in JavaScript that I have run through JSLint a few times. In the past I received the unexpected++ error, I decided to refactor to make my code more readable. A month or so later JSLint came out with an update and is now showing the warning...

Unexpected expression 'i' in statement position. for (i; i < scope.formData.tabs.length; i = i + 1) {

//See JSLint. for why I pulled out i initialization and i = i+1 instead of i++
//and http://stackoverflow./questions/3000276/the-unexpected-error-in-jslint
var i = 0;
for (i; i < scope.formData.tabs.length; i += 1) {
    scope.formData.tabs[i].show = false; // hide all the other tabs 

    if (scope.formData.tabs[i].title === title) {
        scope.formData.tabs[i].show = true; // show the new tab 
    }
}

Reverting to var i = 0 and i++ does not get improve the warnings, JSLint just stops processing.

• javascript
• jslint

• 4 There's no reason to have that i there in the first part of the for loop, if you do the declaration & initialization elsewhere then just leave that part blank and keep the semicolon- – SeinopSys Commented May 15, 2015 at 17:04
• Removing that causing warnings directly in Visual Studio and shows as Unexpected 'for'. and Expected ';' and instead saw ')'. in JSLint. I am pretty sure the for needs all three ponents to work correctly. – JabberwockyDepiler Commented May 15, 2015 at 17:09
• Visual Studio is a terrible IDE in my persional opinion. for(;i<x;i++) statement; is a perfectly valid for loop, no matter what it tells you. – SeinopSys Commented May 15, 2015 at 17:12
• 1 If you still don't believe me, see the MDN docs for the for loop – SeinopSys Commented May 15, 2015 at 17:23
• 1 Where did you see that var i=0; for (i; ... is preferred over var i; for (i=0; ... in JSLint? I didn't necessarily see that in the linked question, nor at the JSLint instructions. – ruffin Commented May 18, 2015 at 18:05

2 Answers 2

Looks like the follow-up problem isn't [just?] due to JSLint being in beta. It's because Crockford no longer allows for statements by default. Looks like I'm going to need to set aside a weekend to read the new instructions and source. Strange things are afoot at the Circle K, man.

The most important new feature of ES6 is proper tail calls. This has no new syntax, so JSLint doesn't see it. But it makes recursion much more attractive, which makes loops, particularly for loops, much less attractive.

Then this in the /*jslint */ directive section's main table:

Description: Tolerate for statement
Option: for
Meaning: true if the for statement should be allowed.

There's a little more explanation below the table:

JSLint does not remend use of the for statement. Use array methods like forEach instead. The for option will suppress some warnings. The forms of for that JSLint accepts are restricted, excluding the new ES6 forms.

So to make this lint in the new JSLint, you need at least this code (with the for directive set):

/*jslint white:true, for:true */
/*global scope, title */

function test()
{
    "use strict";
    var i;

    for (i=0; i < scope.formData.tabs.length; i = i + 1) {
        scope.formData.tabs[i].show = false; // hide all the other tabs 

        if (scope.formData.tabs[i].title === title) {
            scope.formData.tabs[i].show = true; // show the new tab 
        }
    }
}

Note that I did still have to move i's initialization, so you might still have an issue worth reporting. I'll also admit I'm with Stephen at the question you link; I'm not sure why i+= 1 is better. But now it looks like a hard requirement. No plusplus option.

Notice also that if the code isn't wrapped in a function (I wrapped in test, above), you'll get Unexpected 'for' at top level., which is a new error.

EDIT: It seems as if I was mistaken. See ruffin's answer for a more detailed explanation.

It seems as if the problem is with jslint.. Remember, it is still in beta. If you use the old version (old.jslint.), the problem seems to go away.

Here's the output for old.jslint.:
It's mostly all about scope not being defined... etc.

Here's the output from jslint.: It's about scope not getting defined... etc AND

Unexpected 'for'.

along with

Unexpected expression 'i' in statement position.

For now, I suppose you should just use the old version of jslint..