This is my first time integrating TypeScript into my project.
When attempting to access something using window.document.getElementById(), I keep encountering the error:
Type error: Object is possibly 'null'. TS2531
I've looked online for a solution but haven't found anything that fully resolves this issue. It's puzzling since window should never be null.
When utilizing TypeScript, it is important to note that
window.document.getElementById("foobar")null.
If you are confident that the #foobar element does indeed exist in your DOM, you can demonstrate this certainty to TypeScript by using the ! operator.
// Utilize "!" at the end of line
const myAbsolutelyNotNullElement = window.document.getElementById("foobar")!
Alternatively, you can incorporate a runtime nullable check to satisfy TypeScript's requirements
const myMaybeNullElement = window.document.getElementById("foobar")
myMaybeNullElement.nodeName // <- error!
if (myMaybeNullElement === null) {
alert('oops');
} else {
// Following the nullable check, TypeScript will no longer raise complaints
myMaybeNullElement.nodeName // <- no error
}
const item = window.document.getElementById("xyz123");This code will either return an HTMLElement or null
If you have used a similar statement like this:
window.document.getElementById("xyz123").valueYou may encounter TypeScript errors if the value is not accessible, prompting you to explicitly check for null before accessing it.
To prevent this issue, you can modify your code as follows:
const item = window.document.getElementById("xyz123");
if (item !== null) {
alert(item.value);
}
The reason is that you need to specify the type.
let toggleSwitch = document.getElementById("toggleFilter") as HTMLInputElement;
toggleSwitch.checked = true;
It's important to ensure that your
window.document.getElementById("id_name")!const element = window.document.getElementById("id_name")!;
if(element){
console.log(element);
}
Typescript is raising an issue regarding the object returned by the execution of window.document.getElementById, which in your case might be null.
To address this, you could disable this warning by using the strictNullChecks flag in your tsconfig.json, although I do not recommend doing so.
Alternatively, you can follow the suggestions provided in other responses or, starting from Typescript 3.7, utilize the Optional Chaining syntax to streamline your code:
obj?.doSometething(); //this is fine and will not try to perform 'doSomething'.
obj?.prop = 'plop'; //not recommended as it does not work with assignments.
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