How to use document.getElementById() method in TypeScript?
document.getelementbyid(...) is null
document.getelementbyid not working
document.getelementbyid in typescript
getelementbyid returns null
document getelementbyid vs viewchild
document.getelementbyid returning null
I am trying to reset HTML Form in order to clear all the values in the input fields using;
But I can use that in typescript, it's giving me an error saying
document.getElementById('myForm') may be null
How can I solve this issue?
Typescript will force you to check the value is not null if you use the
strictNullChecks option (or
strict which includes
strictNullChecks). You can either perform the test or use a not null assertion (!). Also you will need to use a type assertion to assert the html element is an
HTMLFormElement as by default it will be just an
reset is present only
Just an assertion Assertion:
(document.getElementById('myForm') as HTMLFormElement).reset();
Assertion with check (recommended):
let form = document.getElementById('myForm') if(form) (form as HTMLFormElement).reset();
Not null assertion (if you want to access just
Document.getElementById(), Usage notes. The capitalization of "Id" in the name of this method must be correct for the code to function; getElementByID() is The getElementById() method returns the element that has the ID attribute with the specified value. This method is one of the most common methods in the HTML DOM, and is used almost every time you want to manipulate, or get info from, an element on your document. Returns null if no elements with the specified ID exists.
There are different fixes for this. You can edit your tsconfig.json and add
to it. This will disable the strict null checks.
If you are absolutely sure that the element exists, you could also use
! to tell typescript that your id will always be there
Or if you want to make sure to never get an error because the element indeed doesn't exist, check for its existance
const el = document.getElementById('myForm'); if (el) el.reset();
Try a check on the element. Something like:
var myForm = document.getElementById('myForm'); if(myForm) myForm.reset();
Handbook - DOM Manipulation, Using the DOM method "document.getElementById()" the text inside the paragraph tag is accessed and the value is displayed in the output. The first line of the TypeScript code uses a global variable document, inspecting the variable shows it is defined by the Document interface from the lib.dom.d.ts file. The code snippet contains calls to two methods, getElementById and createElement. Document.getElementById. The definition for this method is as follows:
Handling DOM level events in Angular with typescript, Note: In HTML5, the "name" attribute is deprecated and has been replaced by the "id" attribute for many elements. Use the document.getElementById() method (method) Document. getElementById (elementId: string): HTMLElement It looks like we have found our disconnect - at runtime there are two possible values (an HTMLElement object or null ), but at compile time TypeScript believes the return value will always be of one single type , HTMLElement .
- Also, if
myFormis not found, then it could indeed be a problem. TS doesn't know the layout of your page.
- If you’re really sure the element exists, you could work around the default typing using
- I'm using it with AngularJs, It's the controller where I can find
myForm, But the problem is its giving me an error saying document.getElementById('myForm') may be null before compiling.
document.getElementById('myForm')!this will work but later if i add
[ts] Property 'reset' does not exist on type 'HTMLElement'. any.
- Non null assertions are forbidden in ts > 3.4.5, just use assertion (the first one).
- @Takatalvi Why are they forbidden? This is news to me, could you please provide some docs to that? Maybe you have a lint rule forbidding them but they are still a fuly supported part of the language
- @Takatalvi a tslint rule is just a lint rule. One can opt into it or not. There are plenty of code bases that do not opt into forbidding this operator, the TS compiler team being one of them. There is also a TS lint rule that forces you to specify all types which I personally find to be a horrible idea. Opting blindly into every rule is not a good idea.
- Thanks for the clarification. I misunderstood the warning.
document.getElementById('myForm')!this will pass the null error but later if i add
.reset()then it says
[ts] Property 'reset' does not exist on type 'HTMLElement'. any