javascript 无法获取未定义或空引用的属性“长度”
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Unable to get property 'length' of undefined or null reference
提问by GIVE-ME-CHICKEN
I have the following code - All it does it grabs the value in a text box, performs regex on the string and then counts how many asterisks are in the string value:
我有以下代码 - 它所做的一切都是在文本框中获取值，对字符串执行正则表达式，然后计算字符串值中有多少个星号：
var textBoxValue = $(textbox).val();
function countHowManyWildCards(stringToSearch) {
var regex = new RegExp(/\*/g);
var count = stringToSearch.toString().match(regex).length;
return count;
}
if (countHowManyWildCards(textBoxValue) > 1) {
//Other code
}
The code seems to work, but there is an error appearing on:
代码似乎可以工作，但出现错误：
stringToSearch.toString().match(regex).length;
The error states:
错误指出：
Unable to get property 'length' of undefined or null reference
无法获取未定义或空引用的属性“长度”
But I am unclear why the code works, but I still have this error? Can someone fill me in on why this happening?
但我不清楚为什么代码有效，但我仍然有这个错误？有人可以告诉我为什么会发生这种情况吗？
回答by anubhava
Since matchis failing and not returning any array as a result calling .lengthon it will throw that error.
由于match失败并且不返回任何数组，因此调用.length它会抛出该错误。
To fix this you can use:
要解决此问题，您可以使用：
var count = (stringToSearch.match(regex) || []).length;
to take care of the case when matchfails. || []will return an empty array when match fails and [].lengthwill get you 0.
处理match失败时的情况。|| []匹配失败时将返回一个空数组，并[].length会得到你0。
回答by GOTO 0
The return value of .match(regex)is nullif there are no matches.
.match(regex)的返回值是null如果没有匹配项。
回答by vinu
stringToSearch.toString().match(regex) will return null if stringToSearch does not contain any '*'
stringToSearch.toString().match(regex) 将返回 null 如果 stringToSearch 不包含任何 '*'
