How to Retrieve the Value of <input type=date> Using TypeScript

Question

How to Retrieve the Value of <input type=date> Using TypeScript

I am currently developing a survey website and need assistance with retrieving user input for two specific dates: the start date and end date. I aim to make the survey accessible only between these dates, disabling the "take survey" button after the end date has passed. However, before proceeding to code this functionality, I have encountered an issue trying to display the user's input in the console log. Below is my current setup:

HTML:

<input formControlName="startDate" id="startDate" type="date"/>

TypeScript:

 const startDate = document.getElementById('startDate') as HTMLInputElement | null;

console.log(startDate?.value);

Unfortunately, the console.log displays 'undefined'. Any suggestions on how to resolve this issue?

document.querySelector('input').addEventListener('change', () => {
  const startDate = document.getElementById('startDate')
  
  console.log(startDate.value);
})

<input formControlName="startDate" id="startDate" type="date" />

javascript angular typescript

Answer 1

Answer №1

To prevent binding the callback function to the wrong element, you can implement a type guard function that checks if the selected element is actually an input element:

Explore this code snippet in the TS Playground

function isInputElement (
  value: Element | null | undefined,
): value is HTMLInputElement {
  return value?.tagName === 'INPUT';
}

const startDateInput = document.getElementById('startDate');

if (isInputElement(startDateInput)) {
  // If the condition evaluates to true,
  // then the compiler is certain that it's an <input>:
  startDateInput.addEventListener('change', () => {
    console.log(startDateInput.value);
                            //^? (property) HTMLInputElement.value: string
  });
}
else {
  // The element either didn't exist
  // or it wasn't an <input>
}

JavaScript compiled from the TS playground:

"use strict";
function isInputElement(value) {
    return value?.tagName === 'INPUT';
}
const startDateInput = document.getElementById('startDate');
if (isInputElement(startDateInput)) {
    startDateInput.addEventListener('change', () => {
        console.log(startDateInput.value);
    });
}
else {
}

<input formControlName="startDate" id="startDate" type="date" />

Answer 2

To prevent binding the callback function to the wrong element, you can implement a type guard function that checks if the selected element is actually an input element:

Explore this code snippet in the TS Playground

function isInputElement (
  value: Element | null | undefined,
): value is HTMLInputElement {
  return value?.tagName === 'INPUT';
}

const startDateInput = document.getElementById('startDate');

if (isInputElement(startDateInput)) {
  // If the condition evaluates to true,
  // then the compiler is certain that it's an <input>:
  startDateInput.addEventListener('change', () => {
    console.log(startDateInput.value);
                            //^? (property) HTMLInputElement.value: string
  });
}
else {
  // The element either didn't exist
  // or it wasn't an <input>
}

JavaScript compiled from the TS playground:

"use strict";
function isInputElement(value) {
    return value?.tagName === 'INPUT';
}
const startDateInput = document.getElementById('startDate');
if (isInputElement(startDateInput)) {
    startDateInput.addEventListener('change', () => {
        console.log(startDateInput.value);
    });
}
else {
}

<input formControlName="startDate" id="startDate" type="date" />

Answer 3

Answer №2

Using vanilla JavaScript in an Angular project that utilizes TypeScript might not be the most efficient or recommended approach. It deviates from the Angular methodology.

Based on your provided code snippet, it seems you are implementing ReactiveForms. This suggests that within the component's logic, you have likely created the entire form as a JavaScript object, similar to the example below:

...
  myForm!: FormGroup;  

  constructor(private fb: FormBuilder) {}

  ngOnInit(): void {
    this.myForm = this.fb.group({
       startDate: ['', Validators.required]
    });
  }

If your goal is to retrieve the value of the startDate control, simply access it through the form object like so:

getDate(): Date | undefined {
  return this.myForm.get('startDate')?.value; // could be undefined
}

To monitor input changes whenever the user modifies the value, utilize valueChanges as demonstrated below:

ngOnInit(): void {
  this.myForm.get('startDate').valueChanges.subscribe((theDate) => console.log(theDate));
}

In scenarios where you aren't using ReactiveForms but need to select an input element, you can employ a local reference for the input and access it via ViewChild, such as depicted here:

<input type="text" #myName/>

...
 @ViewChild('myName') myName!: ElementRef;

 getName(): string {
   return this.myName.nativeElement.value;
 }

I highly recommend referencing the official documentation if you encounter specific challenges within an Angular project.

Answer 4

Using vanilla JavaScript in an Angular project that utilizes TypeScript might not be the most efficient or recommended approach. It deviates from the Angular methodology.

Based on your provided code snippet, it seems you are implementing ReactiveForms. This suggests that within the component's logic, you have likely created the entire form as a JavaScript object, similar to the example below:

...
  myForm!: FormGroup;  

  constructor(private fb: FormBuilder) {}

  ngOnInit(): void {
    this.myForm = this.fb.group({
       startDate: ['', Validators.required]
    });
  }

If your goal is to retrieve the value of the startDate control, simply access it through the form object like so:

getDate(): Date | undefined {
  return this.myForm.get('startDate')?.value; // could be undefined
}

To monitor input changes whenever the user modifies the value, utilize valueChanges as demonstrated below:

ngOnInit(): void {
  this.myForm.get('startDate').valueChanges.subscribe((theDate) => console.log(theDate));
}

In scenarios where you aren't using ReactiveForms but need to select an input element, you can employ a local reference for the input and access it via ViewChild, such as depicted here:

<input type="text" #myName/>

...
 @ViewChild('myName') myName!: ElementRef;

 getName(): string {
   return this.myName.nativeElement.value;
 }

I highly recommend referencing the official documentation if you encounter specific challenges within an Angular project.

How to Retrieve the Value of <input type=date> Using TypeScript

Answer №1

Answer №2

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