将使用中无法避免的全局变量缓存到局部
使用缓存全局变量可使 JS 代码在执行的时候会具有更高的执行性能，关于缓存全局变量其实指的就是在程序执行过程中针对全局变量的使用无法避免的。将大量可以重复使用的全局变量，放置到局部作用域当中从而达到一种缓存的效果。
<html>
<body>
<input type="button" value="btn" id="btn1" />
<input type="button" value="btn" id="btn2" />
<input type="button" value="btn" id="btn3" />
<input type="button" value="btn" id="btn4" />
<input type="button" value="btn" id="btn5" />
<input type="button" value="btn" id="btn6" />
<input type="button" value="btn" id="btn7" />
<input type="button" value="btn" id="btn8" />
<input type="button" value="btn" id="btn9" />
<input type="button" value="btn" id="btn10" />
<input type="button" value="btn" id="btn11" />
<input type="button" value="btn" id="btn12" />
<input type="button" value="btn" id="btn13" />
<input type="button" value="btn" id="btn14" />
<input type="button" value="btn" id="btn15" />
<input type="button" value="btn" id="btn16" />
<input type="button" value="btn" id="btn17" />
<input type="button" value="btn" id="btn18" />
<input type="button" value="btn" id="btn19" />
<input type="button" value="btn" id="btn20" />
<input type="button" value="btn" id="btn21" />
<input type="button" value="btn" id="btn21" />
<input type="button" value="btn" id="btn22" />
<input type="button" value="btn" id="btn23" />
<input type="button" value="btn" id="btn24" />
<script>
function getBtn() {
let oBtn1 = document.getElementById('btn1')
let oBtn2 = document.getElementById('btn2')
let oBtn3 = document.getElementById('btn3')
let oBtn4 = document.getElementById('btn4')
let oBtn5 = document.getElementById('btn5')
let oBtn6 = document.getElementById('btn6')
let oBtn7 = document.getElementById('btn7')
let oBtn8 = document.getElementById('btn8')
let oBtn9 = document.getElementById('btn9')
let oBtn10 = document.getElementById('btn10')
let oBtn11 = document.getElementById('btn11')
let oBtn12 = document.getElementById('btn12')
let oBtn13 = document.getElementById('btn13')
let oBtn14 = document.getElementById('btn14')
let oBtn15 = document.getElementById('btn15')
let oBtn16 = document.getElementById('btn16')
let oBtn17 = document.getElementById('btn17')
let oBtn18 = document.getElementById('btn18')
let oBtn19 = document.getElementById('btn19')
let oBtn20 = document.getElementById('btn20')
let oBtn21 = document.getElementById('btn21')
let oBtn22 = document.getElementById('btn22')
let oBtn23 = document.getElementById('btn23')
let oBtn24 = document.getElementById('btn24')
}
function getBtn2 () {
let obj = document
let oBtn1 = obj.getElementById('btn1') let oBtn2 = obj.getElementById('btn2') let oBtn3 = obj.getElementById('btn3') let oBtn4 = obj.getElementById('btn4') let oBtn5 = obj.getElementById('btn5') let oBtn6 = obj.getElementById('btn6') let oBtn7 = obj.getElementById('btn7') let oBtn8 = obj.getElementById('btn8') let oBtn9 = obj.getElementById('btn9') let oBtn10 = obj.getElementById('btn10') let oBtn11 = obj.getElementById('btn11') let oBtn12 = obj.getElementById('btn12') let oBtn13 = obj.getElementById('btn13') let oBtn14 = obj.getElementById('btn14') let oBtn15 = obj.getElementById('btn15') let oBtn16 = obj.getElementById('btn16') let oBtn17 = obj.getElementById('btn17') let oBtn18 = obj.getElementById('btn18') let oBtn19 = obj.getElementById('btn19') let oBtn20 = obj.getElementById('btn20') let oBtn21 = obj.getElementById('btn21') let oBtn22 = obj.getElementById('btn22') let oBtn23 = obj.getElementById('btn23') let oBtn24 = obj.getElementById('btn24')
}
</script>
</body>
</html>
