1. js實(shí)現(xiàn)動(dòng)畫
<!DOCTYPE html><html lang="en"><head> <meta charset="UTF-8"> <title>animate</title> <style> .ball { width: 40px; height: 40px; margin-bottom: 5px; border-radius: 20px; } .ball1 { background: red; } .ball2 { background: blue; } .ball3 { background: yellow; } </style></head><body> <div class="ball ball1" style="margin-left: 0"></div> <div class="ball ball2" style="margin-left: 0"></div> <div class="ball ball3" style="margin-left: 0"></div> <script> var ball1 = document.querySelector(".ball1"); var ball2 = document.querySelector(".ball2"); var ball3 = document.querySelector(".ball3"); function animate(ball, left, callback) { setTimeout(function () { var marginLeft = parseInt(ball.style.marginLeft, 10); if (marginLeft === left) { callback && callback(); } else { if (marginLeft < left) { marginLeft += 2; } else { marginLeft -= 2; } ball.style.marginLeft = marginLeft + "px"; animate(ball, left, callback); } }, 13); } animate(ball1, 100, function () { animate(ball2, 200, function () { animate(ball3, 300, function () { animate(ball1, 200, function () { animate(ball3, 200, function () { animate(ball2, 180, function () { animate(ball2, 220, function () { animate(ball2, 200, function () { console.log("over"); }) }) }) }) }) }) }) }); </script></body></html>上述代碼就可以實(shí)現(xiàn)一個(gè)動(dòng)畫。注意下面幾點(diǎn)：
•動(dòng)畫的實(shí)現(xiàn)往往依賴于setTimeout。
•注意ele.style.marginLeft如果開始能夠獲取，必須從元素的style中設(shè)置了才能獲取，否則獲取不到。
•利用callback可以實(shí)現(xiàn)雖然使用了setTimeout還能串行執(zhí)行。
但是這產(chǎn)生了回調(diào)地獄，代碼簡單點(diǎn)還好說，一旦代碼復(fù)雜了，我們將很難處理其中的邏輯。所以這時(shí)就可以用到es6中的promise了。
Promise的寫法如下：
<!DOCTYPE html><html lang="en"><head> <meta charset="UTF-8"> <title>animate</title> <style> .ball { width: 40px; height: 40px; margin-bottom: 5px; border-radius: 20px; } .ball1 { background: red; } .ball2 { background: blue; } .ball3 { background: yellow; } </style></head><body> <div class="ball ball1" style="margin-left: 0"></div> <div class="ball ball2" style="margin-left: 0"></div> <div class="ball ball3" style="margin-left: 0"></div> <script> var ball1 = document.querySelector(".ball1"); var ball2 = document.querySelector(".ball2"); var ball3 = document.querySelector(".ball3"); function promiseAnimate(ball, left) { return new Promise(function (resolve, reject) { function animate(ball, left) { setTimeout(function () { var marginLeft = parseInt(ball.style.marginLeft, 10); if (marginLeft === left) { resolve(); } else { if (marginLeft < left) { marginLeft += 2; } else { marginLeft -= 2; } ball.style.marginLeft = marginLeft + "px"; animate(ball, left); } }, 13); } animate(ball,left); }); } promiseAnimate(ball1, 500) .then(function () { return promiseAnimate(ball2, 200); }) .then(function () { return promiseAnimate(ball3, 300); }) .then(function () { return promiseAnimate(ball1, 200); }) .then(function () { return promiseAnimate(ball3, 200); }) .then(function () { return promiseAnimate(ball2, 180); }) .then(function () { return promiseAnimate(ball2, 220); }) .then(function () { return promiseAnimate(ball2, 200); }) </script></body></html>
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