I need to create the following array dynamically, for example:
var data = { point: [
{ x:5, y:8 },
{ x:8, y:10},
]};
console.log(data.point[0].x); // 5 n=0
console.log(data.point[1].y); // 10 n=1
At some point my application needs to expand the array to more than 2 items (n=0, n=1). Please let me know how to do that (i.e. n = 9 ).
You could use Array.push method to add element to an array.
var point = {x:1,y:1};
data.point.push(point);
you can use method 'push' like this code
var data = { point: [
{ x:5, y:8 },
{ x:8, y:10},
]};
console.log(data.point[0].x); // 5 n=0
console.log(data.point[1].y); // 10 n=1
data.point.push({x:4,y:3});
console.log(JSON.stringify(data.point));
You could do something like this:
var data = {'points' : []};
function addPoint(x, y) {
data.points.push({'x' : x, 'y' : y});
}
function getPoint(index) {
return data.points[index];
}
addPoint(10, 20);
addPoint(5, 3);
var p = getPoint(1);
alert(p.x + ", " + p.y); //alerts => "5, 3"
This would work for any arbitrary number of points.
Update
To clear the array
function clearPoints() {
data.points = [];
}
Update 2
These little functions will work okay if you have a simple page. If this points handling is going to end up being part of a larger system, it may be better to do something like this:
var data = {
'points' : [],
addPoint : function(x, y) {
this.points.push({
'x' : x,
'y' : y
});
},
getPoint : function(index) {
return this.points[index];
},
clearPoints : function() {
this.points = [];
},
removePoint : function(index) {
this.points.splice(index, 1);
}
};
Example usage:
alert(data.points.length); // => 0
data.addPoint(1, 2);
data.addPoint(8, 12);
data.addPoint(3, 7);
alert(data.points.length); // => 3
var p = data.getPoint(2); //p = {x:3, y:7};
data.removePoint(1);
alert(data.points.length); // => 2
data.clearPoints();
alert(data.points.length); // => 0
It may allow you to keep your point handling a little cleaner and easier to use and update.
You can either use the push() function as stated, or add additional items to the array using an index, which is preferred in the Google Style Guide. The latter method does require that you have a pointer to the last index.
Note that since assigning values to an array is faster than using push() you should use assignment where possible.
for(var i=lastIndex; i < numOfNewPoints; i++){
data.point[i] = {x:4, y:3};
}
push(). If you want to insert at front, useunshift().