rem.js

//  带有一个px作为单位
var rem = {
    px: 1
};

var _timeoutId = 0
var _timeout = 0
var _resizeCallbacks = []
var _maxPx

rem.init = function(dw, maxPx){
    dw = dw || 640;
    _maxPx = maxPx || 0.8
    var doResize = function () {
        var vw = window.innerWidth;
        rem.px = vw / dw;
        if(rem.px > _maxPx) {
            rem.px = _maxPx
        }
        document.querySelector('html').style.fontSize = 100 * rem.px + 'px';
        _timeoutId = 0

        _resizeCallbacks.forEach((cb) => {
            cb.callback.call(cb.scope)
        })
    };

    doResize();
    window.addEventListener('resize', function () {
        if(_timeoutId) {
            window.clearTimeout(_timeoutId);
        }

        _timeoutId = window.setTimeout(doResize, _timeout)
    });
};

rem.registerResize = function(callback, scope) {
    for(var cb of _resizeCallbacks) {
        if(cb.callback == callback || cb.scope == scope){
            return;
        }
    }

    _resizeCallbacks.push({
        callback: callback,
        scope: scope
    })
}

rem.unregisterResize = function(callback, scope) {
    for(var cb of _resizeCallbacks) {
        if(cb.callback == callback || cb.scope == scope){
            _resizeCallbacks.splice(_resizeCallbacks.indexOf(cb), 1)
        }
    }
}

//  导出 rem
export default rem;