JavaScript - what is the most efficient way to get first item from associative array?

Since associative arrays in JavaScript are objects, there isn't really a first or last element.

You can hope to acquire the order that the elements were saved by the parser and there's no guarantee for consistency.

However, if you want the first key to come up, here is an example function:

// ONLINE-RUNNER:browser;

function getKey(object) {
    for (var property in object) {
        return property;
    }
}


// Usage example

var associativeArray = {
    key1: 'value1',
    key2: 'value2',
};

console.log(getKey(associativeArray));

or if you want to avoid inheritance properties:

// ONLINE-RUNNER:browser;

function getKey(object) {
    for (var property in object) {
        if (object.propertyIsEnumerable(property)) {
            return property;
        }
    }
}


// Usage example:

var associativeArray = {
    key1: 'value1',
    key2: 'value2',
};

console.log(getKey(associativeArray));