IF语句中的javascript变量范围 [英] javascript variable scope in the IF statement

问题描述

在if语句中声明和赋值的变量是仅在if块中还是在整个函数内可见？

Are variables declared and assigned in an "if" statement visible only within that "if" block or within the whole function?

我是否在以下代码中执行此操作？ （似乎工作，但多次声明var结构似乎很尴尬）任何更清洁的解决方案？

Am I doing this right in the following code? (seems to work, but declaring "var structure" multiple times seems awkward) any cleaner solutions?

    function actionPane(state) {
    if(state === "ed") {
        var structure = {
            "element" : "div",
            "attr" : {
                "class" : "actionPane"
            },
            "contains" : [{
                "element" : "a",
                "attr" : {
                    "title" : "edit",
                    "href" : "#",
                    "class" : "edit"
                },
                "contains" : ""
            }, {
                "element" : "a",
                "attr" : {
                    "title" : "delete",
                    "href" : "#",
                    "class" : "delete"
                },
                "contains" : ""
            }]
        }
    } else {
        var structure = {
            "element" : "div",
            "attr" : {
                "class" : "actionPane"
            },
            "contains" : [{
                "element" : "a",
                "attr" : {
                    "title" : "save",
                    "href" : "#",
                    "class" : "save"
                },
                "contains" : ""
            }, {
                "element" : "a",
                "attr" : {
                    "title" : "cancel",
                    "href" : "#",
                    "class" : "cancel"
                },
                "contains" : ""
            }]
        }
    }
    return structure;
}

推荐答案

1）对于整个功能范围，可见变量。因此，您只应声明一次。

1) Variables are visible for the whole function scope. Therefore, you should only declare them once.

2）您不应在示例中将变量声明两次。我建议在函数顶部声明变量，然后稍后设置值：

2) You should not declare the variable twice in your example. I'd recommend declaring the variable at the top of the function, then just setting the value later:

function actionPane(state) {
    var structure;
    if(state === "ed") {
        structure = {    
            ...

关于JavaScript的优秀反馈，我强烈建议使用Douglas Crockford的 JSLint 。它将扫描您的代码以查找常见错误，并找到清理建议。

For excellent feedback on JavaScript, I highly recommend using JSLint by Douglas Crockford. It will scan your code for common errors, and find suggestions for cleanup.

我还建议您阅读小书 JavaScript：The Good Parts 。它包含许多编写可维护JS代码的技巧。

I also recommend reading the small book JavaScript: The Good Parts. It contains a lot of tips for writing maintainable JS code.

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