What is the implementation in ionic 2 to avoid code repetition?

You can do this by creating components on Ionic2.

Example 1: link

Example 2: I made a progress bar component. To do so I had to create a new component:

ionic g component progress-bar

Edit the files as needed:

components/progress-bar/progress-bar.ts

import { Component, Input } from '@angular/core';

@Component({
    selector: 'progress-bar',
    templateUrl: 'progress-bar.html'
})
export class ProgressBarComponent {
    @Input('progress')
    progress: number;

    constructor() { }

}

components/progress-bar/progress-bar.html

<div class="progress-outer">
    <div class="progress-inner" [style.width]="progress + '%'">
        {{progress}}%
    </div>
</div>

components/progress-bar/progress-bar.scss

progress-bar {
    .progress-outer {
        width: 96%;
        margin: 10px 2%;
        padding: 3px;
        text-align: center;
        background-color: #f4f4f4;
        border: 1px solid #dcdcdc;
        color: #fff;
        border-radius: 20px;
    }

    .progress-inner {
        min-width: 15%;
        white-space: nowrap;
        overflow: hidden;
        padding: 5px;
        border-radius: 20px;
        background-color: #COR PRIMARIA DO SEU APP
    }
}

Then declare it globally:

app/app.module.ts

import { ProgressBarComponent } from '../components/progress-bar/progress-bar'

@NgModule({
    declarations: [
...
        ProgressBarComponent
    ],
...
    entryComponents: [
...
        ProgressBarComponent
    ],
...
})

Now just use where you'd like to apply:

pages/exemplo/exemplo.html

...
<ion-content padding>
    <progress-bar [progress]="progressoUpload" *ngIf="iniciadoUpload"></progress-bar>
...

To receive and send parameters between the components there are two important decorators @Input and @Output. Unfortunately I will not be able to LINKAR the documentation for their use. But in my example it has @Input