js-proportional zoom on mobile

//Let the size of text and labels be scaled proportionally with the size of the screen
var html = document.getElementsByTagName('html')[0];
/*Get the width of the screen*/
var width = window.innerWidth;
/* 640 100 320 50 */
var fontSize = 100 / 750 * width ;
/* set fontsize */

html.style.fontSize = fontSize + 'px';
window.onresize = function() {
    var html = document.getElementsByTagName('html')[0];
    /*Get the width of the screen*/
    var width = window.innerWidth ;
    /* 640 100 320 50 */
    var fontSize = 100 / 750 * width;
    /*set fontsize*/
    html.style.fontSize = fontSize + 'px';

}