常用的工具函数，保持更新

1、浏览器环境检测

// 对象是否有 __proto__?
export const hasProto = '__proto__' in {}

// 浏览器环境
export const inBrowser = typeof window !== 'undefined'
export const inWeex = typeof WXEnvironment !== 'undefined' && !!WXEnvironment.platform
export const weexPlatform = inWeex && WXEnvironment.platform.toLowerCase()
// 浏览器ua
export const UA = inBrowser && window.navigator.userAgent.toLowerCase()
export const isIE = UA && /msie|trident/.test(UA)
export const isIE9 = UA && UA.indexOf('msie 9.0') > 0
export const isEdge = UA && UA.indexOf('edge/') > 0
export const isAndroid = (UA && UA.indexOf('android') > 0) || (weexPlatform === 'android')
export const isIOS = (UA && /iphone|ipad|ipod|ios/.test(UA)) || (weexPlatform === 'ios')
export const isChrome = UA && /chrome\/\d+/.test(UA) && !isEdge 
export const isPhantomJS = UA && /phantomjs/.test(UA)  
export const isFF = UA && UA.match(/firefox\/(\d+)/) // 火狐

2、js类型终极判断

	Object.prototype.toString.call(变量)

3、原生复制

const copyToClipboard = str => {
    const el = document.createElement('textarea');
    el.value = str;
    el.setAttribute('readonly', '');
    el.style.position = 'absolute';
    el.style.left = '-9999px';
    document.body.appendChild(el);
    const selected = document.getSelection().rangeCount > 0 
        ? document.getSelection().getRangeAt(0) 
        : false;
    el.select();
    document.execCommand('copy');
    document.body.removeChild(el);
    if (selected) {
        document.getSelection().removeAllRanges();
        document.getSelection().addRange(selected);
    }
};

// Example
copyToClipboard('Lorem ipsum'); // 'Lorem ipsum' copied to clipboard.

4. 获取当前页面的滚动位置

const getScrollPosition = (el = window) => ({
    x: el.pageXOffset !== undefined ? el.pageXOffset : el.scrollLeft,
    y: el.pageYOffset !== undefined ? el.pageYOffset : el.scrollTop
});

// Example
getScrollPosition(); // {x: 0, y: 200}

5. 平滑滚动到页面顶部

const scrollToTop = () => {
    const c = document.documentElement.scrollTop || document.body.scrollTop
    if (c > 0) {
        window.requestAnimationFrame(scrollToTop);
        window.scrollTo(0, c - c / 8);
    }
};

// Example
scrollToTop();

6. 检查指定元素是否出现在视口范围内

const elementIsVisibleInViewport = (el, partiallyVisible = false) => {
    const { top, left, bottom, right } = el.getBoundingClientRect();
    const { innerHeight, innerWidth } = window;
    return partiallyVisible 
        ? ((top > 0 && top < innerHeight) || (bottom > 0 && bottom < innerHeight)) && ((left > 0 && left < innerWidth) || (right > 0 && right < innerWidth))
        : top >= 0 && left >= 0 && bottom <= innerHeight && right <= innerWidth;
};

// Examples
elementIsVisibleInViewport(el); // (not fully visible)
elementIsVisibleInViewport(el, true); // (partially visible)