Change text properties during first occurrence in (nested) for loop

Hi, I am trying to change text properties only on a first occurrence in for loop as shown on a code sample below:

      for (let j = 0; j < countRows; j++) {
        console.log(j)
        const row = figma.createFrame()
            row.clipsContent = false
            row.name = 'Row ' + (j+1)
            row.layoutMode = "VERTICAL"
            row.primaryAxisSizingMode = "AUTO"
            row.counterAxisSizingMode = "AUTO"
            column.appendChild(row)
          
          const rowTextFrame = figma.createFrame()
          rowTextFrame.clipsContent = false
          rowTextFrame.name = 'Text ' + (j+1)
          rowTextFrame.layoutMode = "VERTICAL"
          rowTextFrame.primaryAxisSizingMode = "AUTO"
          rowTextFrame.counterAxisSizingMode = "AUTO"
          rowTextFrame.paddingTop = 10
          rowTextFrame.paddingBottom = 10
          rowTextFrame.paddingLeft = 14

           row.appendChild(rowTextFrame)

          // Generate text

          if (j = 0) {
            const rowText = figma.createText();
            rowText.fontName = { family: "Open Sans", style: "Bold" }
            rowText.characters = "Headline";
            rowTextFrame.appendChild(rowText);  
          } else {
            const rowText = figma.createText();
            rowText.fontName = { family: "Open Sans", style: "Regular" }
            rowText.characters = "Edit me";
            rowTextFrame.appendChild(rowText);  
           } 

I added console.log(j) to see the output, so I am using my if conditional right

And then I added condition if (j = 0) (because the first occurrence would be at 0 always), but when executed Figma will freeze and console output looks like this.

It gets stuck on the next loop and whole Figma freezes and I need to manually close it.
What am I doing wrong? Why I cannot use simple IF conditional to execute different code on first for loop occurrence?