Understanding the Ticker Function in JavaScript

Ticker is running text that is often used in digital signage applications or as promotional media. This text can display information such as news, advertisements, or announcements in an attention-grabbing way. Running text is usually implemented with HTML and CSS, and can be operated without JavaScript, although many software also provide this feature for better scheduling and control.

This article discusses how the ticker function works in JavaScript, which I came across in a challenge on Codewars. This function allows us to create a scrolling text effect using JavaScript.

What are Tickers?

Ticker is text that moves horizontally, which is often used in various applications to display continuously updated information, such as the latest news, announcements, or advertisements. These effects can be found on digital screens or electronic notice boards, and can generally be implemented using HTML, CSS, and JavaScript.

The ticker function in JavaScript which we will discuss below, provides a solution for creating dynamic running text effects in your web application.

The following is the ticker function code that we will discuss:

const ticker = (text, width, tick) => {
  const display = ' '.repeat(width);  // 1
  text = display + text + display;    // 2
  tick = tick % (text.length - width); // 3
  return text.slice(tick, tick + width); // 4
}

Explanation of ticker function

This function has three parameters:

• text: The text you want to display.
• width: The desired display width, i.e. how many characters will be displayed at one time.
• tick: The shift position of the text, which determines which text will be displayed when the function is called.

The following is a technical explanation of each step in this function:

1. Creating Spaces to Wrap Text

const display = ' '.repeat(width);

In the first step, we create an empty string containing spaces as large as the width using the repeat() method. The repeat() function will repeat the specified character (in this case a space) the number of times specified by width.

Example:
If width is 5, then the display variable will contain the string ' ' consisting of 5 spaces.

2. Adding Spaces Around Text

text = display + text + display;

In the second step, we add display strings (spaces) at the front and back of the text (text). This ensures that the text has free space on both sides, providing a place for the text to move (scroll) without being cut off.

Example:
Suppose the given text is 'Hello' and the width is 5. Then after this line, the text will be:

const ticker = (text, width, tick) => {
  const display = ' '.repeat(width);  // 1
  text = display + text + display;    // 2
  tick = tick % (text.length - width); // 3
  return text.slice(tick, tick + width); // 4
}

With this, there is enough empty space on the left and right of the text for smoother movement.

3. Calculating Text Movement Position

const display = ' '.repeat(width);

In the third step, we use the modulus operator (%) to ensure that the tick value is within a valid range and does not exceed the length of the text that has been wrapped in spaces.

The text.length - width value gives the total length of the wrapped text (including spaces) minus the width of the display we want to display (width). This ensures that the text shift specified by the tick does not exceed the displayable text length.

Example:
If the length of the text after adding spaces is 15 (for example, ' Hello '), and the width is 5, then text.length - width becomes 10. That is, we only need to ensure that the ticks are in the range 0 to 9. This ensures that the movement of the text is constant valid without any missing parts.

4. Retrieves a Substring to Display

text = display + text + display;

In the last step, we use the slice() method to take part of the text string, starting from the tick position to the tick width position. The slice() function returns the portion of the string that corresponds to that position.

Example:
For example, if tick = 3 and width = 5, then the code slice(3, 8) will produce the substring 'Hello' from the string ' Hello '.

In this way, we display parts of the text with a length that matches the width. Each time this function is called with a different tick value, the displayed text will shift, creating a movement or scrolling effect.

Example of Using the Ticker Function

Let's see an example of using this function in code:

'     Hello     '

The process that occurs is:

1. display = ' ' (5 spaces).
2. Modified text: ' Hello World '.
3. The tick value = 3, and the length of the text after wrapping is 18. With width = 5, we know that ticks can range from 0 to 13.
4. The slice(3, 8) function will return the substring 'Hello'.

If we increase the tick value on the next call, the text will move further and the part of the text that appears will change.

How Can Text Move?

The movement effect is created because every time we call the ticker function, the tick value will change. As the tick value increases, the portion of the text displayed also changes. This gives the effect of movement because the tick scrolls the text dynamically.

To test this effect further, we can call the ticker function in a loop by periodically increasing the tick value, for example using setInterval() to update the display every few seconds.

If you're interested in trying a similar challenge, I discovered this function via Codewars, and it's a fun exercise to improve your JavaScript programming skills.

Good luck, and I hope this article is useful in understanding how the ticker effect works in JavaScript!

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