Dividing Vertices

my vertex buffer has positions which are not normalised … ie

gl.bufferData(gl.ARRAY_BUFFER, vertices2,gl.STATIC_DRAW);

var posBuffer = gl.createBuffer();

var vertices2 = new Float32Array([-15.000,30.256,-3.893,17.370 etc … ]);

i want to know how i can divide every element of my array by 3 or any other factor so that the vertices will fit into my canvas … what it the javascript program to get the no. of elements in my array and divide all of them by a certain factor … any help would be appreciated … thank you …