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<!DOCTYPE html>
<html>
<title>JavaScript +=运算符示例 - 基础教程(div.cn)</title>
<body>
<h1>JavaScript +=运算符</h1>
<script>
var a = 20;
a += 30; // 等同 a = a + 30
document.write(a);
</script>
</body>
</html>
