Typescript Error: The object doesn't recognize the property 'files' as part of the HTMLElement type

Question

Typescript Error: The object doesn't recognize the property 'files' as part of the HTMLElement type

I am trying to implement an upload feature for my Apps using IONIC.

Below is the HTML code snippet I have written:

<input ion-button block type="file" id="uploadBR">
<input ion-button block type="file" id="uploadIC">
<button ion-button block (click)="upload()">Confirm Claim Restaurant</button>

This is the upload() function that I have defined:

upload(){   
   let BR = document.getElementById('uploadBR').files[0]
   let IC = document.getElementById('uploadIC').files[0]
   console.log(BR)
   console.log(IC)    
 }

The functionality seems to work in regular HTML, but it encounters issues with IONIC.

Upon building the App, an error message pops up saying

Typescript Error: Property 'files' does not exist on type 'HTMLElement'.

Could you please guide me on whether I am approaching this correctly or if I need to modify it while working with typescript?

Thank you.

angular typescript ionic-framework

Answer 1

Answer №1

To access the file, you must explicitly declare it as an HTMLInputElement since files is specifically a property of the input element.

let chosenFile = (<HTMLInputElement>document.getElementById('uploadBR')).files[0];

Answer 2

To access the file, you must explicitly declare it as an HTMLInputElement since files is specifically a property of the input element.

let chosenFile = (<HTMLInputElement>document.getElementById('uploadBR')).files[0];

Answer 3

Answer №2

When working on a React.js project, it can be necessary to utilize the 'as' keyword for type casting as the <> syntax is incompatible with .tsx files.

const selectedFile = (document.getElementById(id) as HTMLInputElement).files[0];

Answer 4

When working on a React.js project, it can be necessary to utilize the 'as' keyword for type casting as the <> syntax is incompatible with .tsx files.

const selectedFile = (document.getElementById(id) as HTMLInputElement).files[0];

Answer 5

Answer №3

If you're unsure about the type, it's better to verify it instead of just casting:

const br = document.getElementById('uploadBR');

if (!(br instanceof HTMLInputElement)) {
    throw new Error("Make sure it's an HTMLInputElement");
}

This approach prevents runtime errors caused by typos or changes in the HTML structure. TypeScript may not catch these issues if you rely solely on casting.

To enhance clarity, you can create an assertion function:

function assertHTMLInput(el: any): asserts el is HTMLInputElement {
    if (!(el instanceof HTMLInputElement)) {
        throw new Error("Expected an input element");
    }
}

Implementation Example:

let BR = document.getElementById("uploadBR");
let IC = document.getElementById("uploadIC");
assertHTMLInput(BR);
assertHTMLInput(IC);

// ✅ Properly typed
console.log(BR.files[0]);
console.log(IC.files[0]);

Answer 6

If you're unsure about the type, it's better to verify it instead of just casting:

const br = document.getElementById('uploadBR');

if (!(br instanceof HTMLInputElement)) {
    throw new Error("Make sure it's an HTMLInputElement");
}

This approach prevents runtime errors caused by typos or changes in the HTML structure. TypeScript may not catch these issues if you rely solely on casting.

To enhance clarity, you can create an assertion function:

function assertHTMLInput(el: any): asserts el is HTMLInputElement {
    if (!(el instanceof HTMLInputElement)) {
        throw new Error("Expected an input element");
    }
}

Implementation Example:

let BR = document.getElementById("uploadBR");
let IC = document.getElementById("uploadIC");
assertHTMLInput(BR);
assertHTMLInput(IC);

// ✅ Properly typed
console.log(BR.files[0]);
console.log(IC.files[0]);

Typescript Error: The object doesn't recognize the property 'files' as part of the HTMLElement type

Answer №1

Answer №2

Answer №3

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