javascript嵌套对象数组的数组

Question

I keepy getting TypeError: testsession.testset[0].athletes is undefined - i have tried lots of different ways, is it not possible to have an array of arrays of objects

 var testsession = {}; var testsetname = {}; var testset = []; testsession.testsetname = testsetname; testsession.testsetname = "week9"; testsession.testset = testset; testsession.testset.push("400M"); testsession.testset.push("800M"); var athletes = []; var Time = "49.2"; var AthleteID = "a92"; var athlete = { "AthleteID": AthleteID, "Time": Time}; //console.log(pointer); testsession.testset[0].athletes = athletes; testsession.testset[0].athletes.push(athlete) console.log(testsession.testset[0].athletes[0]); 

Answer 1

When you try to access testsession.testset[0] that entry is a string. You maybe at least would like to set testsession.testset[0] = {}; before accessing its members.

Answer 2

The testset[0] is a string. Make it an object

var testsession = {};
var testsetname = {};
var testset = [];
testsession.testsetname = testsetname;
testsession.testsetname = "week9";
testsession.testset = testset;

//Earlier you pushed 400m directly which is a string hence causing the error later on
testsession.testset.push({distance: "400M"});
testsession.testset.push({distance: "800M"});

var athletes = [];
var Time = "49.2";
var AthleteID = "a92";
var athlete = { "AthleteID": AthleteID, "Time": Time};
//console.log(pointer);
testsession.testset[0].athletes = athletes;
testsession.testset[0].athletes.push(athlete)
console.log(testsession.testset[0].athletes[0]);

Answer 3

testsession.testset[0] is a primitive value, a string.

The following statement will therefore not have the effect you may think it has:

testsession.testset[0].athletes = athletes;

What happens here? The primitive at the left has no athletes property, but JavaScript will coerce it to a String object, then assign that property to that temporary String object, which then disappears into oblivion.

So it is like that assignment never happened: testsession.testset[0] will remain a primitive value, and primitive values have no properties.

When you read the athletes property, the same will happen again: JavaScript coerces it to a String object, only to find that object has no athletes property, and so you get undefined .

Answer 4

I think you are working code like this.

<script >

var testsession = {};
testsession.testset = [];
testsession.testset.push({testsetname:"week9"});
testsession.testset[0].list = [];

testsession.testset[0].list.push({distance:"400M"});
testsession.testset[0].list[0].athletes = [];
testsession.testset[0].list[0].athletes.push({ AthleteID:  "a92", Time: "49.2"});

testsession.testset[0].list.push({distance:"900M"});
testsession.testset[0].list[1].athletes = [];
testsession.testset[0].list[1].athletes.push({ AthleteID:  "a93", Time: "99.2"});

console.log(testsession);

</script>

and result will be like that:

"{"testset":[{"testsetname":"week9","list":[{"distance":"400M","athletes":[{"AthleteID":"a92","Time":"49.2"}]},{"distance":"900M","athletes":[{"AthleteID":"a93","Time":"99.2"}]}]}]}"