修改函数内的变量 [英] Modify a variable inside a function

问题描述

假设我有一个内联脚本标记，其代码非常简单，如下所示

Lets say I have an inline script tag that has a very simple code as follows

(function() {
 var test = "This is a simple test";

 function modifyTest(s) {
  s = "Modified test text";
 };

 modifyTest(test);
 console.log(test) //Will still display "This is a simple test"

 })();

但是，如果我使用 test = modifyTest（test）;
更改已应用我的问题是这个。
这是在函数内部修改javascript变量的唯一方法，这意味着我必须总是这样做

However if i use test = modifyTest(test); the change is applied my question is this. Is this the only way to modify a variable in javascript inside a function, meaning i must always do

source = function（source ）; 为了改变函数内部的变量，

source = function(source); inorder to alter a variable inside a function,

或者我错过了一个阻止我完成此操作的范围概念？

or am i missing a scope concept that is preventing me from accomplishing this?

推荐答案

modifyTest 函数实质上是创建一个名为的本地函数级变量取值;该变量仅存在于函数范围内，因此修改它不会影响外部作用域。

The modifyTest function is essentially creating a local, function-level variable called s; that variable only exists within the scope of the function, so modifying it will not effect external scope.

如果要修改外部作用域，则不会使用参数：

If you want to modify the external scope, you would not use an argument:

var test = "This is a simple test";
function modifyTest(){
    test = "modified test text";
}
console.log(test);   // This is a simple test
modifyTest();
console.log(test);   // Modified test text

不是说你可以修改通过引用传递的对象，所以你可以修改某些属性：

Not that you can modify an object passed by reference, so you can modify something's properties:

var o = { test: 'This is a simple test' };
function modifyTest(x){
    x.test = 'modified test text';
}
modifyTest(o);
console.log(o.test);   // modified test text

您甚至可以传入名称您要修改的属性：

You could even pass in the name of the property you wish to modify:

var o = { test: 'This is a simple test' };
function modifyTest(x, name){
    x[name] = 'modified test text';
}
modifyTest(o, 'test');
console.log(o.test);    // modified test text

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