Total noob here, I'm currently studying regex in javascript. I have a function that is supposed to pick numbers between 0 and 9 from a string. The function works fine as long as the variable it searches has letters or numbers, however when a null value is entered it gives out the following error:

Uncaught: TypeError: Cannot read property 'toString' of null

How can I fix this? Thank you in advance.

Here is the code:

var lause  = "s0m3 p30pl3";
function tulostanumerot();
var numerot = /[0-9]/g;
   var testi = numerot.test(0-9);

   var setti = lause.match(numerot);
   if (testi === true) {
    console.log(setti.toString());
}
   else {
   console.log("Ei numeroita!");
};

Total noob here, I'm currently studying regex in javascript. I have a function that is supposed to pick numbers between 0 and 9 from a string. The function works fine as long as the variable it searches has letters or numbers, however when a null value is entered it gives out the following error:

Uncaught: TypeError: Cannot read property 'toString' of null

How can I fix this? Thank you in advance.

Here is the code:

var lause  = "s0m3 p30pl3";
function tulostanumerot();
var numerot = /[0-9]/g;
   var testi = numerot.test(0-9);

   var setti = lause.match(numerot);
   if (testi === true) {
    console.log(setti.toString());
}
   else {
   console.log("Ei numeroita!");
};

• javascript
• regex
• null

Share Improve this question Follow asked Aug 1, 2021 at 11:44 jope1994jope1994 2111 silver badge22 bronze badges 3

• 2 This part does not look correct var testi = numerot.test(0-9); – The fourth bird Commented Aug 1, 2021 at 11:49
• 2 The function declaration is incorrect; there's no function body. – Pointy Commented Aug 1, 2021 at 11:51
• can you provide a minimal reproducible example showing the error, the code you provided doesn't produce the type error you described in your question – Nick Parsons Commented Aug 1, 2021 at 12:01

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4 Answers 4

Sorted by: Reset to default 2

The String.prototype.match() returns null if no matches are found.

So, you have two options to handle this

1. check if setti have a truthy value, you can that like this if(setti).
2. Use Optional chaining (?.) like setti?.toString(), .

A few notes about your code:

• The method test() takes a string argument, which makes this not correct var testi = numerot.test(0-9);

• The code is not inside the function function tulostanumerot();

• You can omit testi at all, and only use setti

• Note that match() returns either an array or null, so you can use if (setti) { instead of checking for true

The code might look like

function tulostanumerot() {
    var numerot = /[0-9]/g;
    var setti = lause.match(numerot);

    if (setti) {
        console.log(setti.toString());
    } else {
        console.log("Ei numeroita!");
    }
}
tulostanumerot();

function tulostanumerot(lause) {
  var numerot = /[0-9]/g;
  var setti = lause.match(numerot);

  if (setti) {
    console.log(setti.toString());
  } else {
    console.log("Ei numeroita!");
  }
}

[
  "s0m3 p30pl3",
  "",
  "test"
].forEach(v => tulostanumerot(v));

If you do some console.logging you will see that lause.match() returns an array of numbers where the match was found.

In your case:

["0", "3", "3", "0", "3"]

You are getting an error because setti will be null if no matches are found. We can check for it like so.

if (setti) {
   // Setti is not undefined
}

Then if you want to bine the elements into a string you can use .join instead.

if (setti) {
  console.log(setti.join());
} else {
  console.log("Ei numeroita!");
};

Full code:

var lause = "s0m3 p30pl3";

function tulostanumerot() {
  var numerot = /[0-9]/g;
  var setti = lause.match(numerot);
  
  if (setti) {
    console.log(setti.join(""));
  } else {
    console.log("Ei numeroita!");
  };
}

var lause = "s0m3 p30pl3";
tulostanumerot()

var lause = "no numbers here";
tulostanumerot()

There is several ways to check for this. And sould not be hard to find anything online :)

if(lause) //Will check if there is any value to the string, which is a non false value. Example: 0, null, undefined false will all fail this statement

OR

if(typeof lause !== "undefined") //Simple but will also pass Arrays and objects

if(typeof lause  === "string" && typeof lause  === "number") //Will only be passed if matching. So if the variable is a array or object it will not be passed