Using string as object field to reference

Question

This is an example of what I am trying to accomplish and as expected it is not working.

Is there something similar that would work?

var fieldsToCheck = ["a", "b", "c", "d", "e", "f"];

for (var i = 0; i < fieldsToCheck.length; i++){
    var field = fieldsToCheck[counter];
    if (!obj.field) {
         console.log('There is no field of: ' + field);
    }
 }

I originally did this using only if statements for every field, I am wondering whether or not there is a faster way to do this.

obj.a equates to obj["a"] equates to prop = "a"; obj[prop] — Tomalak
– Tomalak, Commented May 6, 2015 at 21:10

josh · Accepted Answer · 2015-05-06 21:13:54Z

2

You can't access the properties in that way. Since it's a variable, you have to use brackets instead of the dot notation:

var fieldsToCheck = ["a", "b", "c", "d", "e", "f"];

for (var i = 0; i < fieldsToCheck.length; i++){
    var field = fieldsToCheck[counter];
    if (!obj[field]) {
         console.log('There is no field of: ' + field);
    }
 }

When you use the dot notation e.g. obj.field, you're essentially asking if obj has a key field, rather than if obj has a key that is the value of variable field. For anything where you're accessing either unknown or string keys that contain non-variable valid characters like -, you'll have to use the bracket notation like obj[field] or obj["a"].

edited May 6, 2015 at 21:13

answered May 6, 2015 at 21:08

josh

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1 Comment

josh Over a year ago

make sure you accept the answer when you're able to :-)

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