js viewport切换

function setViewport(width) {
    var viewport = document.querySelector("meta[name=viewport]");
    if (viewport) {
        viewport.setAttribute('content', 'width=' + width + ', initial-scale=1');
    } else {
        var mvp = document.createElement('meta');
        mvp.name = "viewport";
        mvp.content = 'width=' + width + ', initial-scale=1';
        document.getElementsByTagName('head')[0].appendChild(mvp);
    }
}

window.addEventListener('resize', function() {
    if (window.innerWidth < 600) {
        setViewport(window.innerWidth);
    } else {
        setViewport('device-width');
    }
});