Get value from Input text field in angular 5

You have wrong bound. You need banana-in-box binding [(ngModel)]="serial" instead of [ngModel]="serial"

() in the binding will update serial model everytime when the input will be changes. From input into model

Single [] will just bind the data of serial if it will be changed by code manually. This will cause to one-way binding - from model into input.

As you guess - together [()] they will make two-way binding.

this is one way binding. from view to controller.

file code.component.html

<label >Code</label>
<input (input)="tcode=$event.target.value" type="text" class="form-control">
<button class="btn btn-success" (click)="submit()">Submit</button>

file code.component.ts

tcode : string;
submit() {
    console.log("the code :" + this.tcode);
}