为什么我不能在 //g 中调用 var；

Question

I am using JavaScript to include textbox and a textarea. Button–calls a function to determine if the string in the textbox is found in the contents of the textarea. Naturally, message to the user if the string was found or not.

Here is my code:

HTML

<textarea id="textbox3" rows="4" cols="50"></textarea>    
<input id="text3" value="" />
<button id="findTextButton" onclick="findText();">
    #2 Find text from textbox in textarea
</button>

JavaScript

function findText() {
    var txtThree = document.getElementById("textbox3").value; 
    var searchWord = document.getElementById("text3").innerHTML.value;
    var globalSearch = /[a-z]/g;
    var deliver = txtThree.match(globalSearch);
    if (searchWord === "") {
        alert("Please Enter Text");
    } else {
        alert(deliver);
    }

}

What I wanted to do was to call to the variable searchWord within the globalSearch function, but it's not letting me do that.

Answer 1

Okay, I think I get what you are wanting....you have a textarea and a text input box. you want to grab the text from the input box and see if there is a match inside the textarea?

You shouldn't need a RegExp unless you intend to do more complicated things. .search() can take RegExp or String.(In this case the value from "text3"). Also your checking if searchWord is empty TOO early. If Javascript runs into ONE error, the whole thing shuts down.

function findText() {
    var txtThree = document.getElementById("textbox3").value; 
    //var searchWord = document.getElementById("text3").innerHTML.value;
    //Take away the .innerHTML above
    var searchWord = document.getElementById("text3").value;
    //var globalSearch = /[a-z]/g;
    //You shouldn't need a RegExp.


    if (searchWord === "") {
        alert("Please Enter Text");
    } else {
        var deliver = txtThree.match(searchWord);
        alert(deliver);
    }
}

I tested this and it works fine for me. IF this is what you were expecting.

I will add that @UselessCode 's answer of using new RegExp(searchWord) is a good idea.

Answer 2

In your code, globalSearch is a Regular Expression literal , it never changes, and will always find the same thing. The expression /[az]/g means find a single character between a and z . The g modifier makes it a global search , meaning that it will keep searching and matching even after it finds the first match.

So, when you run txtThree.match(globalSearch) , match will return an array of single-character strings containing all of the letters in txtThree . For example if txtThree contained the string 'This is a test.' it would return the array [ "h", "i", "s", "i", "s", "a", "t", "e", "s", "t" ] .

You can't use a RegExp literal to search for something that varies. You can however use the RegExp constructor function to generate a dynamic RegExp once you have your searchWord :

var rxSearch = new RegExp(searchWord);
var result = txtThree.match(rxSearch);

You can supply the g modifier as one of the flags in the second parameter to RegExp , but since you are just trying to determine if the string is in there are all, you don't need to keep searching once you find it once.

match either returns an array of matches (a single-element array in this case since we didn't use the g modifier) or null if a match was not found. Since arrays are truthy and nulls are falsey we can use result in an if statement to test whether anything was found:

if (result) {
  alert('Found somthing!');
} else {
  alert('It\'s not there.');
}

As Buildersrejected points out , RegEx is a little bit of overkill for this situation. Were I approaching this problem from scratch I probably would have used indexOf instead:

if (txtThree.indexOf(searchWord) !== -1) {
  alert('Found somthing!');
} else {
  alert('It\'s not there.');
}

In this situation performance doesn't really matter, but if it did, using indexOf would be faster than useing search . indexOf actually takes a normal string as a parameter, search takes a regular expression, if a string is provided it is converted to a regular expression before being used.