title: how to sum 2 numbers in typescript
body: <p>I have this properties</p>
  
  <pre><code>export interface IOurFirstSpfWebPartWebPartProps {
    description: string;
    n1: number;
    n2: number;
  
  }
  </code></pre>
  
  <p>Then I have this method</p>
  
  <pre><code>public render(): void {
      this.domElement.innerHTML = `
        &lt;div class="${styles.ourFirstSpfWebPart}"&gt;
          &lt;div class="${styles.container}"&gt;
            &lt;div class="ms-Grid-row ms-bgColor-themeDark ms-fontColor-white ${styles.row}"&gt;
              &lt;div class="ms-Grid-col ms-u-lg10 ms-u-xl8 ms-u-xlPush2 ms-u-lgPush1"&gt;
                &lt;span class="ms-font-xl ms-fontColor-white"&gt;Welcome to SharePoint!&lt;/span&gt;
                &lt;p class="ms-font-l ms-fontColor-white"&gt;Customize SharePoint experiences using Web Parts.&lt;/p&gt;
                &lt;p class="ms-font-l ms-fontColor-white"&gt;${this.properties.n1} + ${this.properties.n2}&lt;/p&gt;
                &lt;a href="https://github.com/SharePoint/sp-dev-docs/wiki" class="ms-Button ${styles.button}"&gt;
                  &lt;span class="ms-Button-label"&gt;Learn more&lt;/span&gt;
                &lt;/a&gt;
              &lt;/div&gt;
            &lt;/div&gt;
          &lt;/div&gt;
        &lt;/div&gt;`;
    }
  </code></pre>
  
  <p>However this is printing 1+2 instead of 3.</p>