Optimization Suggestions for Javascript

Question

Given this code:

    var minX = minY = maxX = maxY = 0;

    for(var i=0; i<objArray.length; i++){
        if(objArray[i].x < minX){
            minX = objArray[i].x;
        }else if(objArray [i].x > maxX){
            maxX = objArray[i].x;
        }
        if(objArray[i].y < minY){
            minY = objArray[i].y;
        }else if(objArray [i].y > maxY){
            maxY = objArray[i].y;
        }
    }

It works, but I don't think it is very elegant. It is simple logic, but it uses 10 lines of code. Can it be improved?

Answer 1

You could use Math.min and Math.max:

var minX = minY = Number.POSITIVE_INFINITY,
    maxX = maxY = Number.NEGATIVE_INFINITY;

for(var i=0; i<objArray.length; i++){
  minX = Math.min(objArray[i].x, minX);
  minY = Math.min(objArray[i].y, minY);
  maxX = Math.max(objArray[i].x, maxX);
  maxY = Math.max(objArray[i].y, maxY);
}

For loop speed optimization you could store the length to only calculate it once:

for(var i=0, len = objArray.length; i<len; i++){
  //...
}

Check this article for more information about loop optimization.

Another approach, just for "functional fun", since I wouldn't recommend it for performance, could be to separate the x and y values to two arrays using Array.map, and then call the min and max functions with apply:

var allX = objArray.map(function (o) { return o.x; });
var allY = objArray.map(function (o) { return o.y; });

minX = Math.min.apply(Math, allX);
minY = Math.min.apply(Math, allY);
maxX = Math.max.apply(Math, allX);
maxY = Math.max.apply(Math, allY);

How this works?

The apply function is used to call another function, with a given context and arguments, provided as an array. The min and max functions can take an arbitrary number of input arguments: Math.max(val1, val2, ..., valN)

So if we call:

Math.min.apply(Math, [1,2,3,4]);

The apply function will execute:

Math.min(1,2,3,4);

Note that the first parameter, the context, is not important for these functions since they are static, they will work regardless of what is passed as the context.