fit-text.js

function fitTextToview(view) {
    const previousFontSize = view.style.fontSize;
    const originalWidth = innerWidth(view);
    const originalHeight = innerHeight(view);

    var low = 5;
    var high = originalHeight;
    var mid = 0;
    while (low <= high) {
        mid = parseInt((low + high) / 2, 10);
        view.style.fontSize = mid + 'px';
        if (getTextNodeBounds(view).width <= originalWidth
            && getTextNodeBounds(view).height <= originalHeight ) {
            low = mid + 1;
        } else {
            high = mid - 1;
        }
    }

    view.style.fontSize = (mid - 1) + 'px';
    const diff = fontSizeToPx(previousFontSize) -
        fontSizeToPx(view.style.fontSize);

    return diff > 1 || diff < -1;
}

function getTextNodeBounds(textNode) {
    if (document.createRange) {
        var range = document.createRange();
        range.selectNodeContents(textNode);

        if (range.getBoundingClientRect) {
            return range.getBoundingClientRect();
        }
    }
    return null;
}

function fontSizeToPx(fontSize) {
    const pa =  document.body;
    const who = document.createElement('div');

    who.style.cssText = 'display:inline-block; padding:0; line-height:1; position:absolute; visibility:hidden; font-size:'+ fontSize;
    who.appendChild(document.createTextNode('W'));

    pa.appendChild(who);

    const fs = who.offsetHeight;

    pa.removeChild(who);
    return fs;
}

function innerHeight(el) {
    const style = window.getComputedStyle(el, null);
    return el.clientHeight -
        parseInt(style.getPropertyValue('padding-top'), 10) -
        parseInt(style.getPropertyValue('padding-bottom'), 10);
}

function innerWidth(el) {
    const style = window.getComputedStyle(el, null);
    return el.clientWidth -
        parseInt(style.getPropertyValue('padding-left'), 10) -
        parseInt(style.getPropertyValue('padding-right'), 10);
}