add style in angular2 using method

isBold: boolean = false;

  fontSize: number = 40;

  isItalic: boolean = true;

  addCustomStyles() {

      let styles = {

'font-weight': this.isBold ? 'bold' : 'normal',

          'font-style': this.isItalic ? 'italic' : 'normal',

          'font-size.px': this.fontSize

      };

      return styles;

  }

<button style='color:black' [ngStyle]="addCustomStyles()">Test Button</button>