javascript for 循环变量和递归
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javascript for loop variable and recursion
提问by mcot
I have an issue where I have recursion inside of a for loop:
我有一个问题，我在 for 循环内有递归：
function func(node) {
for(var i = 0; i < node.children.length; i++) {
func(node.children[i]);
}
}
Obviously because JavaScript does not have block scope, the same i variable is getting modified each time the function is called. What is the best way to remedy this? Assume regular EcmaScript 3 and I can't use JavaScript 1.7 "let".
显然因为 JavaScript 没有块作用域，所以每次调用函数时都会修改相同的 i 变量。解决此问题的最佳方法是什么？假设常规的 EcmaScript 3 并且我不能使用 JavaScript 1.7“let”。
I know this has been asked before, but the other questions don't seem to show recursion, they show one function call where a closure could be used.
我知道以前有人问过这个问题，但其他问题似乎没有显示递归，它们显示了一个可以使用闭包的函数调用。
回答by MackPro
Cache the length of the array so you would have the following:
缓存数组的长度，以便您拥有以下内容：
function recurse(node) {
for(var i = 0, count = node.children.length; i < count; i++) {
recurse(node.children[i]);
}
}
You should always cache especially when you're dealing with HTMLCollections.
您应该始终缓存，尤其是在处理 HTMLCollections 时。
回答by ?ime Vidas
Just use Crockford's walkTheDOMfunction:
只需使用 Crockford 的walkTheDOM功能：
function walkTheDOM(node, func) {
func(node);
node = node.firstChild;
while (node) {
walkTheDOM(node, func);
node = node.nextSibling;
}
}
You pass in the root node and the function that you want to run for each node, like so:
您传入根节点和要为每个节点运行的函数，如下所示：
var root = document.getElementById('wrap');
walkTheDOM(root, function(node) {
console.log( node.nodeName );
});
Live demo:http://jsfiddle.net/VKWTt/
现场演示：http : //jsfiddle.net/VKWTt/
回答by karthick-sk
Was this facing issue, like during recursion of a function the variable values got replaced. the recursion was inside forloop, so the variables inside the forloop where modified.
这是面临的问题，比如在函数的递归过程中，变量值被替换了。递归在for循环内，因此for循环内的变量被修改。
Use varto declare variables that are modified at recursion.
使用var声明在递归时修改的变量。
回答by Daniel Teichman
You've already defined 'i' as a variable in a broader scope ;)
您已经将 'i' 定义为更广泛范围内的变量；)
回答by Richard Schneider
I think you example should work. The variable iis declared local, so when you recurse a new 'i' is used.
我认为你的例子应该有效。该变量i被声明为本地变量，因此在递归时使用新的“i”。
Javascript does global and local variables!
Javascript 做全局和局部变量！
回答by brymck
I'm a little confused. iis declared locally and so it's notthe same ivariable getting modified. Tested on this very page:
我有点困惑。i是在本地声明的，因此它不是i被修改的同一个变量。在此页面上进行了测试：
var span = document.getElementsByTagName("span")[0];
function func(node) {
for(var i = 0; i < node.children.length; i++) {
console.log([i, node]);
func(node.children[i]);
}
}
func(span);
// returns
// [0, <span id="hlinks-user">...</span>]
// [1, <span id="hlinks-user">...</span>]
// [2, <span id="hlinks-user">...</span>]
// [0, <a href="/users...">...</a>]
// [3, <span id="hlinks-user">...</span>]
// [0, <span title="1 silver...">...</span>]
// [1, <span title="1 silver...">...</span>]
// [4, <span id="hlinks-user">...</span>]
// [0, <span title="7 bronze...">...</span>]
// [1, <span title="7 bronze...">...</span>]
// [5, <span id="hlinks-user">...</span>]
回答by kchr
This worked for me.
这对我有用。
function DragDropChanges(nodeChanged) {
if (nodeChanged.children != null) {
for (i = 0; i < nodeChanged.children.length;
var temp = i;
DragDropChanges(nodeChanged.children[i]);
i = temp;
}
}
}
