AlgorithmsData structuresRuns in your browserReviewed October 1, 2026

Undo / Redo Stack Visualizer

Two stacks remember the past and the undone future of an editor. Interactive step-by-step animation with JavaScript code, complexity and front-end use cases.

Localprivate by defaultFastno sign-up path

Data structuresTime: O(1) per actionSpace: O(history)

Actions (type x / undo / redo)

Undo stack (top is on the right)

Redo stack (top is on the right)

Current text

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Undo/redo uses two stacks. The undo stack remembers earlier states; the redo stack remembers states you undid.

checking
found / in view
ruled out

JavaScript

1class History {
2  constructor() { this.undoStack = []; this.redoStack = []; this.text = ""; }
3  type(ch) {
4    this.undoStack.push(this.text);
5    this.text += ch;
6    this.redoStack = [];
7  }
8  undo() {
9    if (!this.undoStack.length) return;
10    this.redoStack.push(this.text);
11    this.text = this.undoStack.pop();
12  }
13  redo() {
14    if (!this.redoStack.length) return;
15    this.undoStack.push(this.text);
16    this.text = this.redoStack.pop();
17  }
18}

Tip: use the arrow keys to step and the space bar to play or pause.

Loading animation...

Undo / Redo Stack Visualization and Animation

Two stacks remember the past and the undone future of an editor. Before every change, push the current state on the undo stack. Undo pops the undo stack and pushes the current state on the redo stack. Redo does the reverse. A new change clears the redo stack. Time complexity: O(1) per action. Space complexity: O(history). Text editors, drawing tools, form builders and any UI that supports Ctrl+Z.

How to use Undo / Redo Stack Visualizer

Before every change, push the current state on the undo stack.
Undo pops the undo stack and pushes the current state on the redo stack.
Redo does the reverse. A new change clears the redo stack.
Press Play, or step through with the arrow buttons and change the input to see how it reacts.

Questions

What is Undo / Redo Stack?

Two stacks remember the past and the undone future of an editor.

What is the time complexity of Undo / Redo Stack?

Time: O(1) per action. Space: O(history).

Where do front-end developers use Undo / Redo Stack?

Text editors, drawing tools, form builders and any UI that supports Ctrl+Z.

Does this upload my data?

No. This converter runs in your browser for ordinary use, so the input is not sent to a backend by this tool.

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