Find absolute max value in Javascript array

Math.max.apply(null, array.map(Math.abs));

If you target browsers that don't support Array.prototype.map (IE<=8), use the polyfill or a library like sugar.js.

Try this:

var array = [10,20,40,-30,-20,50,-60];
var absMax = array.reduce(function(max, item){
    return Math.max(Math.abs(max),Math.abs(item));
});

How this

var array = [10,20,40,-30,-20,50,-60];    
return Math.max(...array.map(a => Math.abs(a)))