Ways to remedy the "object may be null" issue in TypeScript without turning off strictNullChecks

Question

Ways to remedy the "object may be null" issue in TypeScript without turning off strictNullChecks

Below is my typescript code snippet:

const form  = document.querySelector('form');


if (form != null ) {
    const data = new FormData(form);
    for (const pair of data) {
        console.log(pair);
    }
    // OR
    for (const pair of data.entries()) {
        console.log(pair);
    }
}

document.getElementById("form_file")!.onchange= function(e: Event) {
    let file = (<HTMLInputElement>e.target).files[0];
    }

I have attempted the following:

let file = (<HTMLInputElement>e?.target)?.files[0];

and

let file = (<HTMLInputElement>e!.target)!.files[0];

Is there a way to make it work without having to use the strictNullChecks option in tsconfig?

Best regards

typescript

Answer 1

Answer №1

The issue lies with the files array and not the e.target HTMLInputElement. To solve this, you need to ensure that the files array is not null or undefined before trying to access the first index.

You can achieve this in two ways:

// The "?.[0]" will only access index 0 if `files` is not null or undefined
document.getElementById("form_file")!.onchange= function(e: Event) {
    let file = (e.target as HTMLInputElement).files?.[0];
}

Alternatively, you can do it like this:

document.getElementById("form_file")!.onchange= function(e: Event) {
    let file;

    if((e.target as HTMLInputElement).files){
        file = (e.target as HTMLInputElement).files;
    }
}

Answer 2

The issue lies with the files array and not the e.target HTMLInputElement. To solve this, you need to ensure that the files array is not null or undefined before trying to access the first index.

You can achieve this in two ways:

// The "?.[0]" will only access index 0 if `files` is not null or undefined
document.getElementById("form_file")!.onchange= function(e: Event) {
    let file = (e.target as HTMLInputElement).files?.[0];
}

Alternatively, you can do it like this:

document.getElementById("form_file")!.onchange= function(e: Event) {
    let file;

    if((e.target as HTMLInputElement).files){
        file = (e.target as HTMLInputElement).files;
    }
}

Answer 3

Answer №2

One possible solution to prevent null issues is by properly checking for the existence of elements before accessing them in your code. For example, make sure that the file element and its target files exist before trying to use them.

const input = document.getElementById("form_file");

if (input) {
  input.onChange = function(e: Event) {
    if (e.target && e.target.files) {
      let selectedFile = e.target.files;
    }
  }
}

Answer 4

One possible solution to prevent null issues is by properly checking for the existence of elements before accessing them in your code. For example, make sure that the file element and its target files exist before trying to use them.

const input = document.getElementById("form_file");

if (input) {
  input.onChange = function(e: Event) {
    if (e.target && e.target.files) {
      let selectedFile = e.target.files;
    }
  }
}

Ways to remedy the "object may be null" issue in TypeScript without turning off strictNullChecks

Answer №1

Answer №2

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