JavaScript: match variable to element in array of arrays

Question

I get the first two variables loaded from the backend, then I want to match the brand name I get back and return a two letter code. I put the associated brands in an array of arrays.

It doesn't seem match() is an option, cuz I can't put a variable in regExp().

This didn't work:

if (brand.indexOf(brand_code[i])) {
    bc = brand_code[i][1];
}

This didn't work.

if (brand_code[i][0]===brand)
    bc = brand_code[i][1];
}

This is my latest attempt.

$(document).ready(function() {
    var phone_model='$request.getHeader("x-wurfl-model-name")',
        brand='$request.getHeader("x-wurfl-brand-name")',
        brand_code=[
            ['Alcatel','AL'],
            ['Huawei','HU'],
            ['LG','LG'],
            ['Motorola','MT'],
            ['Samsung','SA'],
            ['Unimax','UX'],
            ['ZTE','ZE']];
    for (var i = brand_code.length - 1; i >= 0; i--) {
        if ($.inArray(brand,brand_code[i])) {
            bc = brand_code[i][1];
        }
    }
    $('.faq .mobile_tutorial a').append(bc+phone_model);
});

This gives me an error of Cannot read property '3' of undefined Where phone_model='Z990g' & brand='ZTE'

Where am I going wrong?

indexOf returns a number of the index, not true/false. if not found, it returns -1. what is the content of brand? — Nina Scholz
– Nina Scholz, Commented Sep 2, 2016 at 21:36

trincot · Accepted Answer · 2016-09-02 22:21:49Z

2

If you would structure your data differently in the variable brand_code, it would become a bit easier:

    brand_code={
        'Alcatel':'AL',
        'Huawei':'HU',
        'LG':'LG',
        'Motorola':'MT',
        'Samsung':'SA',
        'Unimax':'UX',
        'ZTE':'ZE'
    };
    bc = brand_code[brand];
}

This will not need to go through an array. Most JavaScript engines find the match in constant time if you use the object-based lookup above. In ES you can use a Map for the same purpose and with the same efficiency.

About your attempt

$.inArray returns 0 when ZTE matches the first element of an array, so the if condition would be false in that case. But worse, when ZTE is not found, the method returns -1, which makes the if condition true.

So, you would have had better results if you had put:

if ($.inArray(brand,brand_code[i])>-1) {

From the jQuery documentation:

The $.inArray() method is similar to JavaScript's native .indexOf() method in that it returns -1 when it doesn't find a match. If the first element within the array matches value, $.inArray() returns 0.

edited Sep 2, 2016 at 22:21

answered Sep 2, 2016 at 21:38

trincot

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1 Comment

trincot Over a year ago

Thanks. Just be aware that performance-wise this beats filter and reduce, which have to iterate the array. But this is not relevant if the OP's data is small, like it seems to be the case.

Rob M. · Accepted Answer · 2016-09-02 21:42:21Z

2

Use Array.filter to find your match, then you can either check that the result's length > 0 and get result[0][1] from it, or use Array.reduce to return only the code:

// filter down to match and reduce the match to it's code value
brand_code.filter(function(pair) { 
    return pair[0] === brand 
}).reduce(function(out, match) { 
    return match[1]; 
}, '');

OR ES6:

brand_code.filter(pair => pair[0] === brand)
          .reduce((_, match) => match[1], '');

answered Sep 2, 2016 at 21:42

Rob M.

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1 Comment

absynthe minded web smith Over a year ago

This is pretty neat, and I definitely wish ES6 were an option. Sadly, I have to support some devices still using Android 2.3.

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