Dynamically create object keys in IE 11 (Expected identifier, string or number, not a comma issue)

Question

I'm looking for a solution that creates object keys (is that worded correctly?) dynamically.

Arbitrary example, but this works in chrome and firefox

var weeks = {}
for(var i = 0; i < 5; i++){
    $.extend(weeks, {["week" + i] : (i * 2)}
}

//weeks = {"week0":0,"week1":2,"week2":4,"week3":6,"week4":8}

Or alternative arbitrary example

var object = {
  ["a" + 50]: "value"
}

The problem seem to be rooted in the [] operator, but I don't understand how or why this problem only occurs in IE. I have not tested in previous versions to IE11, but I would assume the problem would persist there aswell.

Since the problem seem to be with the [] operator itself, creating my keys in a variable and then shoving that variable into my [] wouldn't do anything to fix the problem, so I seem to be both out of ideas and keywords to google.

So is there a way to dynamically create object keys in IE?

IE11 doesn't support many (if any) of the new ES6 syntaxes. Remember, it's Internet Explorer, not a modern web browser. — gen_Eric
– gen_Eric, Commented May 23, 2016 at 13:48
Extending on @RocketHazmat comment: check "object literal extensions -> computed properties" in the ECMAScript6 compatibility table to check where you can use this syntax. — apokryfos
– apokryfos, Commented May 23, 2016 at 13:50
Why use extend at all? Just use the square bracket notation and assign the property directly? weeks["week" + i] = i * 2; — evolutionxbox
– evolutionxbox, Commented May 23, 2016 at 13:52
Because the actual object I'm looking to create is bigger and more complicated than my examples in the question. My problem is not the use of $.extend. — NachoDawg
– NachoDawg, Commented May 23, 2016 at 13:54
stackoverflow.com/questions/1184123/… - What problem are you actually facing in IE11 then? Does it throw any errors? — evolutionxbox
– evolutionxbox, Commented May 23, 2016 at 14:00

gen_Eric · Accepted Answer · 2016-05-23 13:59:46Z

10

IE11 is not a "modern" web browser in the same way Chrome, Firefox or even Edge is. It doesn't support the new "object literal extensions" from ES6 (ES2015).

The syntax you are using is called "computed property keys", you cannot use it in IE11. You need to do this the "old fashioned" way.

var weeks = {};

for(var i = 0; i < 5; i++){
    var tmp = {};
    tmp["week" + i] = i*2;

    $.extend(weeks, tmp);
}

answered May 23, 2016 at 13:59

gen_Eric

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