function getStyle(dom, key) {
    let style
    if (window.getComputedStyle) {
        style = window.getComputedStyle(dom, null)    // 非IE
    } else {
        style = dom.currentStyle  // IE
    }

    return style[key]
}


function isSupportCalc() {
    let oDiv = document.createElement("div");
    oDiv.style.width = 'calc((100vw / 750) * 100)'

    document.body.appendChild(oDiv)
    let width = getStyle(oDiv, 'width')
    oDiv.remove()

    let diff = 0.5

    width = parseFloat(width)
    let calcWidth = window.screen.availWidth / 750 * 100

    return width && Math.abs(calcWidth - width) < diff
}