title: pdfmake, TypeError: Cannot assign to read only property '0' of string
body: <p>I'm trying to create a PDF using pdfMake with Angular.</p>
  <p>I try to fill an Html table with data from an array. It's an array of object.</p>
  <pre class="lang-js prettyprint-override"><code>export interface OrderDetails {
      orderId?   : number;
      truckMenuId: number;
      price?     : number;
      quantity   : number;
      truckMenu?  : TruckMenu;
      title?: string;
  }
  </code></pre>
  <p>The method below ask an OrderDetails array as parameter.</p>
  <pre class="lang-js prettyprint-override"><code>
    public generatePDF(truck: Truck, orderItems: OrderDetails[]) { 
      let rows: string[] = ['Price', 'Quantity'];
      orderItems.forEach((item) =&gt; {
        var lign = [item.price, item.quantity];
        rows.push(&lt;string&gt;&lt;unknown&gt;lign);
      })  
     
      let docDefinition = {
        content: [
         {  
              text: truck.name,  
              fontSize: 20,  
              alignment: 'center',  
              color: '#FF4F02',
              margin: [0, 20],
            },  
            {  
              text: 'Facture',  
              fontSize: 14,  
              bold: true,  
              alignment: 'Left',  
              decoration: 'underline',  
              color: '#000',
              margin: [0, 20]
           },
            {
            table: {
                     widths: ['*', 70, 50],
                     body: rows
                  }
                },
                 {
                     text: 'Total : ',
                     fontSize: 14,
                     alignment: 'right',
                     margin: [140,20]
                 },
                 {
                     text: 'Thanks',
                     fontSize: 12,
                     margin: [0,20]
                 }
        ],
      }  
      pdfMake.createPdf(docDefinition).open();  
    }   
  </code></pre>
  <p>As you can see, I use a forEach to loop into the array and display the data.</p>
  <p>My problem is that a get an error message but I don't understand why.</p>
  <p><code>TypeError: Cannot assign to read only property '0' of string 'Price'</code></p>
  <p>I found the same error message <a href="https://stackoverflow.com/questions/67968781/typeerror-cannot-assign-to-read-only-property-0-of-string">here</a> but this doesn't solved my problem.</p>
  <p>What's wrong?</p>