The new text style expressions added in After Effects v17 are powerful, but they can be confusing to learn at first.

This is partly because they break one of the unwritten "rules" of expressions, which is that expressions can only set the value for the property they're on.

They break this rule due to the fact an expression on a text layer's sourceText property can set either the text value or the text style.

ts
text.sourceText: {
  // The text content of the string
  value: string,
  // The style properties and methods
  style: object,
}

ts
// The text content
text.sourceText.value; // or text.sourceText
// The style object
text.sourceText.style;

As well as setting a layers style with expressions, you can use text style expressions to retrieve the style properties of a text layer (such as it's font size or leading values).

ts
text.sourceText.style.fontSize;

The style object

These style objects of sourceText properties contain:

• Methods for setting style attributes
• Properties containing the values of the style attributes

For example, the property fillColor and its matching method setFillColor(), or fontSize and setFontSize().

js
text.sourceText.style: {
  fillColor,
  setFillColor(),
  fontSize,
  setFontSize(),
  // etc
}

You can use the methods to modify the style's attributes, and the properties to retrieve the style's attributes.

For example, to set a dynamic font size you would use the setFontSize() method:

js
text.sourceText.style.setFontSize(36);

Chaining methods

Each style method, e.g. setFont(), returns it's style object (it's this value). This means you can chain the methods to set multiple styles.

js
// Chaining the methods
otherStyle
  .setFontSize(36)
  .setLeading(36 * 1.3)
  .setTracking(0);

Setting the text content

Since you set the style by returning a style object on a sourceText property, that means you can't also return a value for the sourceText.value (the text content).

js
const otherStyle = otherLayer.text.sourceText.style;
const textContent = thisLayer.name;
textContent + "this won't be used";
otherStyle; // Overrides the previous line

To get around this, the style object has a setText() method which will set the .value of sourceText.

js
const otherStyle = otherLayer.text.sourceText.style;
const textContent = thisLayer.name;
// Return a new style and new text value
otherStyle.setText(textContent);

By default, returning a style object will not override the existing text content, instead it will keep the original value. You only need to use setText() when setting a new value with expressions.

Getting the style at a character index

You can get the style properties at a specific character index with the sourceText method getStyleAt(characterIndex).

js
text.sourceText.getStyleAt(8).setFontSize(36);

This returns the style object, so you can then chain the other style methods.

By default, a style object returns the style at the first character, so the following two are equal:

js
// Both return the style of the first character
text.sourceText.style;
text.sourceText.getStyleAt(0);

Finding font names

It can be difficult to know which string to use as the font name in setFont, as it differs from the name in the character panel.

js
text.sourceText.style.setFont("RobotoMono-Medium");

To find the correct name of a font you can use the font selector, found in the expression language menu.

This inserts the name of the selected font into your expression.

Creating style objects

You can create an empty style object by using the sourceText method createStyle().

js
const newStyle = text.sourceText.createStyle();
newStyle.setFontSize("90");

For any style properties you haven't set, the value from the original style is used. Because of this, sourceText.createStyle() and sourceText.style are functionally equivalent.

Referencing styles from other layers

You can access the style object of other sourceText properties:

js
const otherStyle = thisComp.layer("text layer").text.sourceText.style;
otherStyle;

Which contains all the style attributes of the sourceText.

You can also use specific properties from the style object:

js
const { fontSize, fillColor } =
  thisComp.layer("text layer").text.sourceText.style;
`The layer has a size ${fontSize} and color ${fillColor}`;

Examples

Setting the style and text

js
const otherSourceText = thisComp.layer("layer name").text.sourceText;
const textValue = `${thisLayer.name} text`;
// Takes the style from another layer
// and sets the text (sourceText.value)
otherSourceText.style.setText(textValue);

Overriding specific style from another layer

js
const { fontSize, leading } =
  thisComp.layer("layer name").text.sourceText.style;
text.sourceText.style.setFontSize(fontSize).setLeading(leading);