var array = [3, 6, 2, 56, 32, 5, 89, 32];
var largest = 0;

for (let i=0; i < array.length; i++) {
    if (array[i] > largest) {
        largest = array[i];
    }
}

console.log(largest);

You can use the apply function, to call Math.max:

var array = [267, 306, 108];
var largest = Math.max.apply(Math, array); // 306

How does it work?

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.

Find the object whose property "Y" has the greatest value in an array of objects

One way would be to use Array reduce..

const max = data.reduce(function(prev, current) {
  return (prev && prev.y > current.y) ? prev : current
}) //returns object

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce
• http://caniuse.com/#search=reduce (IE9 and above)

If you don't need to support IE (only Edge), or can use a pre-compiler such as Babel you could use the more terse syntax.

const max = data.reduce((prev, current) => (prev && prev.y > current.y) ? prev : current)

Note that if you have multiple objects sharing the same max value, it will only return the first matched object.