你可以让所有东西都小写:

var string="Stackoverflow is the BEST";
var searchstring="best";
var result= (string.toLowerCase()).search((searchstring.toLowerCase()));
alert(result);

假设我们想要在字符串变量大海捞针。这里有三个陷阱:

Internationalized applications should avoid string.toUpperCase and string.toLowerCase. Use a regular expression which ignores case instead. For example, var needleRegExp = new RegExp(needle, "i"); followed by needleRegExp.test(haystack). In general, you might not know the value of needle. Be careful that needle does not contain any regular expression special characters. Escape these using needle.replace(/[-[\]{}()*+?.,\\^$|#\s]/g, "\\$&");. In other cases, if you want to precisely match needle and haystack, just ignoring case, make sure to add "^" at the start and "$" at the end of your regular expression constructor.

考虑到第(1)和(2)点，一个例子是:

var haystack = "A. BAIL. Of. Hay.";
var needle = "bail.";
var needleRegExp = new RegExp(needle.replace(/[-[\]{}()*+?.,\\^$|#\s]/g, "\\$&"), "i");
var result = needleRegExp.test(haystack);
alert(result);

取代

var result= string.search(/searchstring/i);

with

var result= string.search(new RegExp(searchstring, "i"));

如果你只是搜索一个字符串，而不是一个更复杂的正则表达式，你可以使用indexOf() -但记住两个字符串都要小写，因为indexOf()是区分大小写的:

var string="Stackoverflow is the BEST"; 
var searchstring="best";

// lowercase both strings
var lcString=string.toLowerCase();
var lcSearchString=searchstring.toLowerCase();

var result = lcString.indexOf(lcSearchString)>=0;
alert(result);

或在单行中:

var result = string.toLowerCase().indexOf(searchstring.toLowerCase())>=0;

我在尝试区分大小写的字符串搜索，我尝试了

 var result = string.toLowerCase().match(searchstring) 

也

var result= string.search(new RegExp(searchstring, "i"));

但我做了一些小修改，对我有用

var result = string.match(new RegExp(searchstring, "i"));

这也可以是小写，大写或组合

ES6 +:

let string="Stackoverflow is the BEST";
let searchstring="best";


let found = string.toLowerCase()
                  .includes(searchstring.toLowerCase());

includes()如果searchString出现在一个或多个位置则返回true，否则返回false。