Javascript 替换空值
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Javascript replace null
提问by petebowden
var p = "null"
var q = null;
(p == q) //false. as Expected.
p.replace(null, "replaced") // outputs replaced. Not expected.
p.replace("null", "replaced") //outputs replaced. Expected.
q.replace(null, "replaced") // error. Expected.
q.replace("null", "replaced") //error. Expected.
Why? Does replace not differentiate between "null"and null?
为什么？替换不区分"null"和null吗？
I ask because I ran into a bug in angularjs:
我问是因为我在 angularjs 中遇到了一个错误：
replace((pctEncodeSpaces ? null : /%20/g), '+');
If for example, someone had a username of "null"and it was used as url, it would be replaced with "+" on any $httpcalls. e.g. GET /user/null.
例如，如果某人的用户名是"null"并且它被用作 url，那么在任何$http调用中它都会被替换为“+” 。例如GET /user/null。
Not that this scenario would occur often, but I'm more curious why replace treats nulland "null"as the same thing. Does replace do a .tostring on nullbefore it does the replacement? Is this just a quirk of Javascript?
并不是说这种情况会经常发生，但我更好奇为什么要替换零食null和"null"作为同一件事。null在替换之前替换是否执行 .tostring ？这只是 Javascript 的一个怪癖吗？
I verified this on both IE and Chrome's implementations of replace.
我在 IE 和 Chrome 的replace.
采纳答案by Russ Cam
Yes, this is expected according to the spec for replace(bolded relevant line, or page 146 of the ECMA-262 final draft). The first argument is checked to see if it is a regex and if not, it has toString()called on it (well, converted to a string somehow).
是的，根据规范replace（粗体相关行，或ECMA-262 最终草案的第 146 页），这是预期的。检查第一个参数以查看它是否是正则表达式，如果不是，则toString()调用它（好吧，以某种方式转换为字符串）。
15.5.4.11
String.prototype.replace(searchValue, replaceValue)Let string denote the result of converting the this value to a string.
Cut for brevity
If
searchValueis not a regular expression, letsearchStringbeToString(searchValue)and search string for the first occurrence ofsearchString. Let m be 0.Cut for brevity
15.5.4.11
String.prototype.replace(searchValue, replaceValue)让 string 表示将 this 值转换为字符串的结果。
为简洁起见
如果
searchValue不是正则表达式，则让searchStringbeToString(searchValue)并搜索字符串以查找第一次出现的searchString。让 m 为 0。为简洁起见
回答by Alnitak
In the ES5 specification for String.prototype.replace:
在ES5 规范中String.prototype.replace：
15.5.4.11 String.prototype.replace (searchValue, replaceValue)
...
If
searchValueis not a regular expression, letsearchStringbeToString(searchValue)and searchstringfor the first occurrence ofsearchString
15.5.4.11 String.prototype.replace (searchValue, replaceValue)
...
如果
searchValue不是正则表达式，让searchStringbeToString(searchValue)并搜索string第一次出现的searchString
So, "".replace(null, XXX)will indeed convert the nullto the string "null"
所以，"".replace(null, XXX)确实会转换null为字符串"null"
Note that ToString()does notmean null.toString()- it's an internal defined operation within the JavaScript interpreter.
请注意，ToString()这并不意味着null.toString()- 它是 JavaScript 解释器中内部定义的操作。
回答by Paul S.
"null".replace(null, "replaced") // outputs replaced. Not expected.
Does replace not differentiate between "null" and null
不替换不区分“空”和空
This is because parameter 1 of replaceis converted to String.
这是因为参数 1replace被转换为String。
''+null === "null"; // true by cast to string
Furthermore, as replacetakes RegExpobjects, you can also think about how
此外，由于replace采用的RegExp对象，你也可以想想如何
RegExp(null).toString() === "/null/"; // true
回答by brunoais
For the not expected one, there's a simple answer. The null is casted to string by the replace() method.
So that is also an expected action
对于意想不到的人，有一个简单的答案。通过 replace() 方法将空值转换为字符串。
所以这也是一个预期的动作
