打字稿 .length 返回未定义

Question

This issue makes me crazy ...

I have this code :

if (control.value==null||control.value == "" || control.value == " " || control.value.length != 5) {
     // do something
}

My problem : control.value.length always returns 'undefined'.

I try to use a string variable like this but the result is the same.

var curVal: string = control.value;
if (curVal==null||curVal== "" || curVal == " " || curVal != 5) {
     // do something
}

Where am I wrong ?

Edit: Precision : my control.value is not null or empty, I test with the value 59000

This code :

console.log(control.value + ' - ' + control.value.length);

log this : 59000 - undefined

EDIT 2 : Thank's you, it's solved. The problem was my control.value was a number and not a string .

Answer 1

I think that the type of your input isn't string but number.

@Component({
  selector: 'my-app',
  template: `
    <div>
      <input type="number" [ngFormControl]="ctrl">
    </div>
  `
})
export class AppComponent {
  constructor() {
    this.ctrl = new Control();
    this.ctrl.valueChanges.subscribe((val) => {
      console.log(val.length);
    });
  }
}

In this case val.length returns undefined since numbers don't have a length attribute.

See this plunkr for more details: https://plnkr.co/edit/5yp5ms9XY5Z3TEE2qYIh?p=preview .

Answer 2

Try Like these

String(control.value).length != 5

OR

control.value.toString().length != 5

Answer 3

In Typescript:

     let a="hello";
     let length=a.toString().length;
     console.log(length);

Output: 5

Answer 4

Sometimes there is this bug on Angular, since version 5.0.0 I think, even when the variable is not a number, I've to convert it to a number to use the '.length' property like below :

if (control.value==null||control.value == "" || control.value == " " || +(control.value.length) != 5) {
 // do something

It may works, just by adding the sign '+' before your var.length like: +(var.length)

Answer 5

I had the same issue before, in my case my object was set with a string with lowercase "s" therefore an Angular primitive. You need to add toString() before the length: control.value.toString().length.