Vue.js xterm.js FitAddon Called Too Early, Terminal Doesn't Resize To The Correct Dimensions

[BrilliantBrilliant is verified member.]

The issue you're experiencing with the xterm.js FitAddon being called too early is a common problem when integrating xterm.js into frameworks like Vue.js. It typically happens because the FitAddon tries to resize the terminal before the DOM element is fully rendered or its dimensions are stable.

Why This Happens

The FitAddon calculates the terminal dimensions based on the size of its container. If the container’s dimensions aren’t finalized (e.g., due to Vue's reactive rendering or layout delays), the terminal won't resize properly.

Solution: Ensure FitAddon is Called at the Right Time

1. Use nextTick

Vue’s nextTick ensures that the DOM is fully updated before executing your code. You can initialize the terminal and call fit() inside a nextTick callback:

import { Terminal } from 'xterm';

import { FitAddon } from 'xterm-addon-fit';



export default {

  mounted() {

    this.$nextTick(() => {

      const terminal = new Terminal();

      const fitAddon = new FitAddon();

      terminal.loadAddon(fitAddon);

     

      const terminalContainer = this.$refs.terminal; // Reference to the terminal's container

      terminal.open(terminalContainer);



      // Call fit after the DOM is ready and container dimensions are stable

      fitAddon.fit();

    });

  }

};

Make sure your template includes the reference:

<div ref="terminal" style="width: 100%; height: 100%;"></div>





---

2. Watch for Container Resizing

If the container's size changes after initialization (e.g., due to window resizing or dynamic layout adjustments), you need to re-fit the terminal. Add a resize listener:

mounted() {

  const terminal = new Terminal();

  const fitAddon = new FitAddon();

  terminal.loadAddon(fitAddon);



  const terminalContainer = this.$refs.terminal;

  terminal.open(terminalContainer);



  // Ensure the terminal is resized correctly after rendering

  this.$nextTick(() => {

    fitAddon.fit();

  });



  // Listen for window resize events

  window.addEventListener('resize', () => {

    fitAddon.fit();

  });

},



beforeDestroy() {

  // Clean up event listeners

  window.removeEventListener('resize', this.onResize);

}





---

3. Set Explicit Container Dimensions

Sometimes, the terminal's parent container might not have proper dimensions. You should ensure its dimensions are explicitly set (e.g., via CSS):

.terminal-container {
  width: 100%;
  height: 100%;
  display: flex;
}

In your template:

<div ref="terminal" class="terminal-container"></div>

---[/CODE]

4. Use Vue’s Lifecycle Events (if needed)

If your terminal is part of a dynamically shown component (e.g., modals or tabs), initialize the FitAddon in the activated lifecycle hook for keep-alive components or when the component becomes visible:

activated() {

  this.$nextTick(() => {

    this.fitAddon.fit(); // Call fit after the component becomes visible

  });

}





---

5. Debounce Resizing

For performance, debounce the resize event handler if the terminal is being resized frequently.

import debounce from 'lodash/debounce';



mounted() {

  const terminal = new Terminal();

  const fitAddon = new FitAddon();

  terminal.loadAddon(fitAddon);



  terminal.open(this.$refs.terminal);



  const onResize = debounce(() => {

    fitAddon.fit();

  }, 100);



  window.addEventListener('resize', onResize);



  this.$nextTick(() => {

    fitAddon.fit();

  });



  this.onResize = onResize; // Save the handler for cleanup

},



beforeDestroy() {

  window.removeEventListener('resize', this.onResize);

}





---

Debugging Checklist

Container Dimensions: Inspect the terminal's container using browser dev tools to ensure it has a width and height.

Timing Issues: Use console.log before and after fitAddon.fit() to verify when it's being called.

Parent Layouts: Ensure parent elements do not have display: none, as it prevents proper sizing.