Apply scrollback via setOption

demo/index.html

@@ -16,7 +16,12 @@ <h1>xterm.js: xterm, in the browser</h1>
         <div id="terminal-container"></div>
         <div>
           <h2>Options</h2>
-          <label><input type="checkbox" id="option-cursor-blink"> cursorBlink</label>
+          <p>
+            <label><input type="checkbox" id="option-cursor-blink"> cursorBlink</label>
+          </p>
+          <p>
+            <label>Scrollback <input type="number" id="option-scrollback" value="1000" /></label>
+          </p>
           <div>
           	<h3>Size</h3>
             <div>

demo/main.js

@@ -8,7 +8,8 @@ var term,
 
 var terminalContainer = document.getElementById('terminal-container'),
     optionElements = {
-      cursorBlink: document.querySelector('#option-cursor-blink')
+      cursorBlink: document.querySelector('#option-cursor-blink'),
+      scrollback: document.querySelector('#option-scrollback')
     },
     colsElement = document.getElementById('cols'),
     rowsElement = document.getElementById('rows');
@@ -28,6 +29,9 @@ colsElement.addEventListener('change', setTerminalSize);
 rowsElement.addEventListener('change', setTerminalSize);
 
 optionElements.cursorBlink.addEventListener('change', createTerminal);
+optionElements.scrollback.addEventListener('change', function () {
+  terminal.setOption('scrollback', parseInt(optionElements.scrollback.value, 10));
+});
 
 createTerminal();
 
@@ -37,7 +41,8 @@ function createTerminal() {
     terminalContainer.removeChild(terminalContainer.children[0]);
   }
   term = new Terminal({
-    cursorBlink: optionElements.cursorBlink.checked
+    cursorBlink: optionElements.cursorBlink.checked,
+    scrollback: parseInt(optionElements.scrollback.value, 10)
   });
   term.on('resize', function (size) {
     if (!pid) {
@@ -78,7 +83,6 @@ function createTerminal() {
   });
 }
 
-
 function runRealTerminal() {
   term.attach(socket);
   term._initialized = true;

src/xterm.js

@@ -405,6 +405,24 @@ Terminal.prototype.setOption = function(key, value) {
   if (!(key in Terminal.defaults)) {
     throw new Error('No option with key "' + key + '"');
   }
+  switch (key) {
+    case 'scrollback':
+      if (this.options[key] !== value) {
+        if (this.lines.length > value) {
+          const amountToTrim = this.lines.length - value;
+          const needsRefresh = (this.ydisp - amountToTrim < 0);
+          this.lines.trimStart(amountToTrim);
+          this.ybase = Math.max(this.ybase - amountToTrim, 0);
+          this.ydisp = Math.max(this.ydisp - amountToTrim, 0);
+          if (needsRefresh) {
+            this.refresh(0, this.rows - 1);
+          }
+        }
+        this.lines.maxLength = value;
+        this.viewport.syncScrollArea();
+      }
+      break;
+  }
   this[key] = value;
   this.options[key] = value;
 };