JavaScript性能优化 - 减少声明及语句数

<html>
<body>
  <div id="box" style="width:100px;height:100px"></div>
  <script>
    // 减少声明优化前
    var oBox = dovument.getElementById('box');
    function test (ele) {
        let w = ele.offsetWidth
        let h = ele.offsetHeight
        return w*h
    }
    // 减少声明优化后
    function test (ele) {
        return ele.offsetWidth * ele.offsetHeight
    }
    console.log(test(oBox))
    // 减少语句数优化前    function test () {
        var name = 'test';
        var age = 18;
        var slogen = 'DBHFHNF';
        return name + age + solgen
    }
    // 减少语句数优化后
    function test () {
        var name = 'test', age = 18 , slogen = 'DBHFHNF';        return name + age + solgen
    }  </script>
</body>
</html>