gsap-utils

gsap.utils

When to Use This Skill

Apply when writing or reviewing code that uses gsap.utils for math, array/collection handling, unit parsing, or value mapping in animations (e.g. mapping scroll to a value, randomizing, snapping to a grid, or normalizing inputs).

Related skills: Use with gsap-core, gsap-timeline, and gsap-scrolltrigger when building animations; CustomEase and other easing utilities are in gsap-plugins.

Overview

gsap.utils provides pure helpers; no need to register. Use in tween vars (e.g. function-based values), in ScrollTrigger or Observer callbacks, or in any JS that drives GSAP. All are on gsap.utils (e.g. gsap.utils.clamp()).

Omitting the value: function form. Many utils accept the value to transform as the last argument. If you omit that argument, the util returns a function that accepts the value later. Use the function form when you need to clamp, map, normalize, or snap many values with the same config (e.g. in a mousemove handler or tween callback). Exception: random() — pass true as the last argument to get a reusable function (do not omit the value); see random()).

// With value: returns the result
gsap.utils.clamp(0, 100, 150); // 100

// Without value: returns a function you call with the value later
let c = gsap.utils.clamp(0, 100);
c(150);  // 100
c(-10);  // 0

Clamping and Ranges

clamp(min, max, value?)

Constrains a value between min and max. Omit value to get a function: clamp(min, max)(value).

gsap.utils.clamp(0, 100, 150); // 100
gsap.utils.clamp(0, 100, -10); // 0

let clampFn = gsap.utils.clamp(0, 100);
clampFn(150); // 100

mapRange(inMin, inMax, outMin, outMax, value?)

Maps a value from one range to another. Use when converting scroll position, progress (0–1), or input range to an animation range. Omit value to get a function: mapRange(inMin, inMax, outMin, outMax)(value).

gsap.utils.mapRange(0, 100, 0, 500, 50);  // 250
gsap.utils.mapRange(0, 1, 0, 360, 0.5);   // 180 (progress to degrees)

let mapFn = gsap.utils.mapRange(0, 100, 0, 500);
mapFn(50);  // 250

normalize(min, max, value?)

Returns a value normalized to 0–1 for the given range. Inverse of mapping when the target range is 0–1. Omit value to get a function: normalize(min, max)(value).

gsap.utils.normalize(0, 100, 50);   // 0.5
gsap.utils.normalize(100, 300, 200); // 0.5

let normFn = gsap.utils.normalize(0, 100);
normFn(50); // 0.5

interpolate(start, end, progress?)

Interpolates between two values at a given progress (0–1). Handles numbers, colors, and objects with matching keys. Omit progress to get a function: interpolate(start, end)(progress).

gsap.utils.interpolate(0, 100, 0.5);       // 50
gsap.utils.interpolate("#ff0000", "#0000ff", 0.5); // mid color
gsap.utils.interpolate({ x: 0, y: 0 }, { x: 100, y: 50 }, 0.5); // { x: 50, y: 25 }

let lerp = gsap.utils.interpolate(0, 100);
lerp(0.5); // 50

Random and Snap

random(minimum, maximum[, snapIncrement, returnFunction]) / random(array[, returnFunction])

Returns a random number in the range minimum–maximum, or a random element from an array. Optional snapIncrement snaps the result to the nearest multiple (e.g. 5 → multiples of 5). To get a reusable function, pass true as the last argument (returnFunction); the returned function takes no args and returns a new random value each time. This is the only util that uses true for the function form instead of omitting the value.

// immediate value: number in range
gsap.utils.random(-100, 100);        // e.g. 42.7
gsap.utils.random(0, 500, 5);        // 0–500, snapped to nearest 5

// reusable function: pass true as last argument
let randomFn = gsap.utils.random(-200, 500, 10, true);
randomFn();  // random value in range, snapped to 10
randomFn();  // another random value

// array: pick one value at random
gsap.utils.random(["red", "blue", "green"]);  // "red", "blue", or "green"
let randomFromArray = gsap.utils.random([0, 100, 200], true);
randomFromArray();  // 0, 100, or 200

String form in tween vars: use "random(-100, 100)", "random(-100, 100, 5)", or "random([0, 100, 200])"; GSAP evaluates it per target.

gsap.to(".box", { x: "random(-100, 100, 5)", duration: 1 });
gsap.to(".item", { backgroundColor: "random([red, blue, green])" });

snap(snapTo, value?)

Snaps a value to the nearest multiple of snapTo, or to the nearest value in an array of allowed values. Omit value to get a function: snap(snapTo)(value) (or snap(snapArray)(value)).

gsap.utils.snap(10, 23);     // 20
gsap.utils.snap(0.25, 0.7);  // 0.75
gsap.utils.snap([0, 100, 200], 150); // 100 or 200 (nearest in array)

let snapFn = gsap.utils.snap(10);
snapFn(23); // 20

Use in tweens for grid or step-based animation:

gsap.to(".x", { x: 200, snap: { x: 20 } });

shuffle(array)

Returns a new array with the same elements in random order. Use for randomizing order (e.g. stagger from "random" with a copy).

gsap.utils.shuffle([1, 2, 3, 4]); // e.g. [3, 1, 4, 2]

distribute(config)

Returns a function that assigns a value to each target based on its position in the array (or in a grid). Used internally for advanced staggers; use it whenever you need values spread across many elements (e.g. scale, opacity, x, delay). The returned function receives (index, target, targets) — either call it manually or pass the result directly into a tween; GSAP will call it per target with index, element, and array.

Config (all optional):

| Property | Type | Description | |----------|------|-------------| | base | Number | Starting value. Default 0. | | amount | Number | Total to distribute across all targets (added to base). E.g. amount: 1 with 100 targets → 0.01 between each. Use each instead to set a fixed step per target. | | each | Number | Amount to add between each target (added to base). E.g. each: 1 with 4 targets → 0, 1, 2, 3. Use amount instead to split a total. | | from | Number \| String \| Array | Where distribution starts: index, or "start", "center", "edges", "random", "end", or ratios like [0.25, 0.75]. Default 0. | | grid | String \| Array | Use grid position instead of flat index: [rows, columns] (e.g. [5, 10]) or "auto" to detect. Omit for flat array. | | axis | String | For grid: limit to one axis ("x" or "y"). | | ease | Ease | Distribute values along an ease curve (e.g. "power1.inOut"). Default "none". |

In a tween: pass the result of distribute(config) as the property value; GSAP calls the function for each target with (index, target, targets).

// Scale: middle elements 0.5, outer edges 3 (amount 2.5 distributed from center)
gsap.to(".class", {
  scale: gsap.utils.distribute({
    base: 0.5,
    amount: 2.5,
    from: "center"
  })
});

Manual use: call the returned function with (index, target, targets) to get the value for that index.

const distributor = gsap.utils.distribute({
  base: 50,
  amount: 100,
  from: "center",
  ease: "power1.inOut"
});
const targets = gsap.utils.toArray(".box");
const valueForIndex2 = distributor(2, targets[2], targets);

See distribute() for more.

Units and Parsing

getUnit(value)

Returns the unit string of a value (e.g. "px", "%", "deg"). Use when normalizing or converting values.

gsap.utils.getUnit("100px");   // "px"
gsap.utils.getUnit("50%");     // "%"
gsap.utils.getUnit(42);        // "" (unitless)

unitize(value, unit)

Appends a unit to a number, or returns the value as-is if it already has a unit. Use when