Typescipt to make use of resize.js. Make sure you added the resize.js in your assets folder and given the reference to your angular-cli in scripts array.

component.ts

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

declare var $: any;
declare var window;

@Component({
    selector: 'app-init',
    templateUrl: './app.component.html'
})
export class AppInit {
    private base64textString: String = "";
    
    handleFileSelect(evt) {
        var files = evt.target.files;
        var file = files[0];
        var resize = new window.resize();
        resize.init();
        
        resize.photo(files[0], 500, 'dataURL', (thumbnail) => {
            file = thumbnail;  
            console.log(file); 
            this.base64textString  = file;
        });
    }
}