[英]many local variables declaration vs one global?
i'm just new javascript biginner, If i need to reuse many times (lets say 20 times) the same variable, from a performance point of view, should i declare it one time as global , or declare it many times in each function context in local scope ( as i heard about ) ? 我只是新的javascript专家,如果我需要重用很多次(比如说20次),那么从性能的角度来看,我应该将其声明为global一次,还是在每个函数上下文中声明多次?在当地(我听说)?
whats case bellow is better ? 什么情况下更好?
caseA : 案例A:
var myvar = document.getElementById('case'); //global
function one(){
myvar.innerHTML = 'newb';
...
}
function two(){
myvar.value = '3';
...
}
caseB : caseB:
function one(){
var myvar = document.getElementById('case'); //local
myvar.innerHTML = 'newb';
...
}
function two(){
var myvar = document.getElementById('case'); //lobal
myvar.value = '3';
...
}
caseC : caseC:
var myvar = document.getElementById('case'); //global
function one(){
var myvar = document.getElementById('case'); //local
myvar.innerHTML = 'newb';
...
}
function two(){
var myvar = document.getElementById('case'); //lobal
myvar.value = '3';
...
}
thx for advises, 劝告,
gui gui
Wrap case A inside a closure 将箱子A包裹在一个封闭物中
(function() {
var myvar = document.getElementById('case');
function one(){
myvar.innerHTML = 'newb';
...
}
function two(){
myvar.value = '3';
...
}
})()
now nothing is in the global scope but you only access the DOM once. 现在,全局范围内没有任何东西,但是您只能访问DOM一次。
The case A must be the best, or if you like object oriented programming you can do : 情况A必须是最好的,否则,如果您喜欢面向对象的编程,则可以这样做:
function MyClass() {
this.element = document.getElementById('case');
this.one = function() {
this.element.innerHTML = 'newb';
}
this.two = function() {
this.element.value = '3';
}
return this;
}
var myCls = new MyClass();
myCls.one();
myCls.two();
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