Get key value of first item in object

Question

I have the following object which defines the end and start times for a paragraph:

var times = {
 "p1": [24.500, 29.268],
 "p2": [29.268, 29.441],
 "p3": [29.441, 29.640]
};

I wish to call updateCurrentParagraph when the paragraph changes:

vid.addEventListener("timeupdate", function() {

    var t = this.currentTime;
    for (var key in times) {
       if (t >= times[key][0] && t < times[key][1])
       {
           updateCurrentParagraph(key);
           return;
       }
    }

    // at end of audio
    if (times[times.length-1][1] == t){
        updateCurrentParagraph(???);
        return;
    }

    updateCurrentParagraph("unknown");
    return;

});

What do I do at ??? to get "p3"?

first you need to define `first_paragraph` before assigning, then add `times.p1=first_paragraph` — Akhil Aravind, Jul 11 '18 at 07:56
do you like to get the key with the greates value of the array? — Nina Scholz, Jul 11 '18 at 08:08

score 0 · Answer 1 · answered Jul 11 '18 at 07:54

0

Just use Object.keys method by passing your object as argument.

var key = Object.keys(times)[0];
var values = times[key]

answered Jul 11 '18 at 07:54

Mihai Alexandru-Ionut

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I dont think this is reliable as key in object doesnt guarantee sequence. – Isaac Jul 11 '18 at 07:55
@Mihai Alexandru-Ionut Would that be Object.keys(times[times.length-1]) for the last key? I've updated my question. – Baz Jul 11 '18 at 08:06
No, for the last key is : `var lastKey = Object.keys(times)[times.length-1]` – Mihai Alexandru-Ionut Jul 11 '18 at 08:08

score 0 · Answer 2 · answered Jul 11 '18 at 08:18

You could save the last key which has the right time for checking after the loop, if the properties are not ordered.

vid.addEventListener("timeupdate", function () {
    var t = this.currentTime,
        last;
    for (var key in times) {
        if (times[key][0] >= t && times[key][1] < t) {
            updateCurrentParagraph(key);
            return;
        }
        if (times[key][1] === t) {
            last = key;
        }
    }

    // at end of audio
    if (last) {
        updateCurrentParagraph(last);
        return;
    }

    updateCurrentParagraph("unknown");
    return;
});

Get key value of first item in object

2 Answers2