Convert a string variable to regular expression in java script?

so I am trying to search a string for a sub string, and apparently, I must u开发者_Go百科se regular expressions with the .search function, this is the code I have

var str = items[i].toLowerCase;
var str2 = document.getElementById("input").value.toLowerCase;

var index = str.search(str2);

Obhiously this doesn't work and I get an error, saying str.search is not a function, how would I go about changing these two strings into regular expressions?

thanks

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Use this:

new RegExp("your regex here", "modifiers");

Take a look into: Using a string variable as regular expression

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add braces to your function calls:

var str = items[i].toLowerCase();
var str2 = document.getElementById("input").value.toLowerCase();
var index = str.search(str2);

otherwise type of "str" is a function, not result of function execution

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your problem is forgetting a set of brackets () -- and as such str and str2 get assigned a function rather than the result of calling that function! Simply change the code:

var str = items[i].toLowerCase();
var str2 = document.getElementById("input").value.toLowerCase();

var index = str.search(str2);

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To use an expression in a RegExp constructor:

var re = new RegExp(str, 'g');

will create a regular expression to match the value of str in a string, so:

var str = 'foo';
var re = new RegExp(str, 'i');

is equivalent to the RegExp literal:

var re = /foo/i;

You can use any expression that evaluates to a valid regular expression, so to match foo at the start of a string:

var re = new RegExp('^' + str, 'i');

The only niggle is that quoted characters must be double quoted, so to match whitespace at the end of a string:

var re = new RegExp('\\s+$');

which is equivalent to:

var re = /\s+$/;