Javascript define variables with names from array

Question

I have a function where several values from a multidimensional array are called very often, like array[idx][3].. In order to save space I want to define variables with these values at the beginning of the function like so:

var na = array[idx][1];
var sc = array[idx][2];
...

I thought it would be faster if it was possible to create an array of variable names -> var tmp = ['na','sc',...];, create a for loop and cycle through the array of names and the multidimensional array, i.e.:

for(i = 0; i = 7, i++){

var tmp[i] = array[idx][i];

}

Is it possible?

Yes it's possible - looks like you have the right code, what's wrong / what's the question? — tymeJV
– tymeJV, Commented Aug 7, 2015 at 15:49
Is it something that can't be easily tested? Somehow you're overwriting the ['na', 'sc'...] in that for-loop. — fuyushimoya
– fuyushimoya, Commented Aug 7, 2015 at 15:50

fuyushimoya · Accepted Answer · 2015-08-07 16:53:07Z

1

You can use array to store keys.
Then use Object to create a key-> value mapping.
Then use either obj.key(if key is fixed) or obj[key](if key is a calculated value) top get the value.
In your jsfiddle for (i = 0; i = 7; i++) { will hang the browser, you should use i < 7 instead of i = 7.

var keys = ['na', 'sc', 'kd', 'wi', 'ki', 'de', 'sh', 'ti'];
var values = {};

var i, key, len;
// Prevent using magic number 7, get the length from the keys.
for (i = 0, len = keys.length; i < len; i++) {
  values[keys[i]] = i;
}
alert(values.na);

Its possible to further shorten the works by Array.prototype.forEach:

// Create map store.
var v = {};
// Loop through the array
['na', 'sc', 'kd', 'wi', 'ki', 'de', 'sh', 'ti'].forEach(function(key, idx) {
    v[key] = idx;
});
alert(v.na);

jsfiddle

Combine with your idx may be dynamic, you can create a function, given the idx and target array, return the object with the keys.

// A list to simulate what you mentioned with array[idx][i].
var demoList = [
    ['na - 0', 'sc - 0', 'kd - 0', 'wi - 0', 'ki - 0', 'de - 0', 'sh - 0', 'ti - 0'],
    ['na - 1', 'sc - 1', 'kd - 1', 'wi - 1', 'ki - 1', 'de - 1', 'sh - 1', 'ti - 1'],
    ['na - 2', 'sc - 2', 'kd - 2', 'wi - 2', 'ki - 2', 'de - 2', 'sh - 2', 'ti - 2'],
    ['na - 3', 'sc - 3', 'kd - 3', 'wi - 3', 'ki - 3', 'de - 3', 'sh - 3', 'ti - 3'],
    ['na - 4', 'sc - 4', 'kd - 4', 'wi - 4', 'ki - 4', 'de - 4', 'sh - 4', 'ti - 4'],
    ['na - 5', 'sc - 5', 'kd - 5', 'wi - 5', 'ki - 5', 'de - 5', 'sh - 5', 'ti - 5'],
    ['na - 6', 'sc - 6', 'kd - 6', 'wi - 6', 'ki - 6', 'de - 6', 'sh - 6', 'ti - 6'],
    ['na - 7', 'sc - 7', 'kd - 7', 'wi - 7', 'ki - 7', 'de - 7', 'sh - 7', 'ti - 7']
];

var getResult = function(idx, array) {
    var v = {};
    // Only create the mapping if input array and array[idx] are both array.
    if (Array.isArray(array) && Array.isArray(array[idx])) {
        ['na', 'sc', 'kd', 'wi', 'ki', 'de', 'sh', 'ti'].forEach(function(key, i) {
            v[key] = array[idx][i];
        });
    }
    return v;
};

var v = getResult(1, demoList);
alert(v.na);

edited Aug 7, 2015 at 16:53

answered Aug 7, 2015 at 15:55

fuyushimoya

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2 Comments

Innerwolf Over a year ago

Well that's not exactly what i wanted, but i could use i.e. v.na, that's shorter. But it's the same length as an array like v[2], would be easier to define also. Other suggestions?

fuyushimoya Over a year ago

I'd like to know more precise about what you wanted. values is just a name so it's ok to change to anything you want if its valid. What do you mean 'it's the same length as an array like v[2]'.

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