Adding structured data to an Array in JavaScript

Question

I am trying to create sample data to test a form Grid. And am using the following function to try and create the data to send to my grid.

// populateFields: Populates data n times a record of data for the SSM form.
// @params: n, fips, products
// @returns: fields
populateFields(n, fips, products) {
    var data = [];
    var fields = this.getFields();


    for(i = 0; i < n; i++) {
        var x = {fields[0]: false, 
        fields[1]: fips[getRandomInt(0, fips.length())], 
        fields[2]: products[getRandomInt(0, products.length())], 
        fields[3]: getRandomInt(0, 100)};
        data.push(x);
    }

    return data;
}

Nothing gets populated when I call it. I get an error saying fields[0]: false needs [ token.

Note: This is part of a class, I don't think that matters. I am not sure if you want to see how I call it.

Is it because of jQuery, as in what I am passing the array to.

One other minor issue: you don't declare your loop counter, i. — Scott Sauyet
– Scott Sauyet, Commented Aug 20, 2018 at 20:17
One question, though: does getFields() return varying results? If so, how do you know that fields[1] has anything to do with "fips" or that fields[2] is related to "products"? — Scott Sauyet
– Scott Sauyet, Commented Aug 20, 2018 at 20:18

Jonas Wilms · Accepted Answer · 2018-08-20 20:33:09Z

5

To use a variable as a property key it has to be enclosed in brackets:

 {
   [fields[0]]: false
   //...
 }

Otherwise it would try to use field[0] as an identifier itself, and some characters like [ arent allowed in identifiers (cause they are used for property access). (They are allowed in property names though, so { "field[0]": false } would work syntactically, but that makes little sense).

edited Aug 20, 2018 at 20:33

answered Aug 20, 2018 at 20:07

Jonas Wilms

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3 Comments

Jonas Wilms Over a year ago

@raxenx glad to help :)

Scott Sauyet Over a year ago

The commentary is slightly misleading. The new(ish) bracket syntax for Object keys allows us to do in a single step what previously took multiple steps. (myObj = { ... }; myObj[fieldName] = value; ...), but it doesn't change what is an allowable property name, Symbols and any Strings. So this is a perfectly acceptable property name: "(ab [no I ^meant cd])!" even though its full of spaces and special characters. Of course that isn't a legal identifier name, but that's a slightly different question than one about object property names.

Jonas Wilms Over a year ago

@scott yup but without the [] or "" its an identifier.

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