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)

Mutates and returns the same array in random order. Shuffle a copy when the original array is state, props, or shared data.

const shuffled = gsap.utils.shuffle([...items]);

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):

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(fn, unit)

Wraps a numeric function and appends a unit to its returned value. Use when a reusable helper should produce CSS values or tween end values.

const wrapX = gsap.utils.unitize(gsap.utils.wrap(0, 300), "px");

wrapX(450); // "150px"
wrapX(-50); // "250px"

splitColor(color, returnHSL?)

Converts a color string into an array: [red, green, blue] (0–255), or [red, green, blue, alpha] (4 elements for RGBA when alpha is present or required). Pass true as the second argument (returnHSL) to get [hue, saturation, lightness] or [hue, saturation, lightness, alpha] (HSL/HSLA) instead. Works with "rgb()", "rgba()", "hsl()", "hsla()", hex, and named colors (e.g. "red"). Use when animating color components or building gradients. See splitColor().

gsap.utils.splitColor("red");                    // [255, 0, 0]
gsap.utils.splitColor("#6fb936");                // [111, 185, 54]
gsap.utils.splitColor("rgba(204, 153, 51, 0.5)"); // [204, 153, 51, 0.5] (4 elements)
gsap.utils.splitColor("#6fb936", true);          // [94, 55, 47] (HSL: hue, saturation, lightness)

Arrays and Collections

selector(scope)

Returns a scoped selector function that finds elements only within the given element (or ref). Use in components so selectors like ".box" match only descendants of that component, not the whole document. Accepts a DOM element or a ref (e.g. React ref; handles .current).

const q = gsap.utils.selector(containerRef);
q(".box");        // array of .box elements inside container
gsap.to(q(".circle"), { x: 100 });

toArray(value, scope?)

Converts a value to an array: selector string (scoped to element), NodeList, HTMLCollection, single element, or array. Use when passing mixed inputs to GSAP (e.g. targets) and a true array is needed.

gsap.utils.toArray(".item");           // array of elements
gsap.utils.toArray(".item", container); // scoped to container
gsap.utils.toArray(nodeList);          // [ ... ] from NodeList

pipe(...functions)

Composes functions: pipe(f1, f2, f3)(value) returns f3(f2(f1(value))). Use when applying a chain of transforms (e.g. normalize → mapRange → snap) in a tween or callback.

const fn = gsap.utils.pipe(
  (v) => gsap.utils.normalize(0, 100, v),
  (v) => gsap.utils.snap(0.1, v)
);
fn(50); // normalized then snapped

wrap(min, max, value?)

Wraps a value into the range min–max (inclusive min, exclusive max). Use for infinite scroll or cyclic values. Omit value to get a function: wrap(min, max)(value).

gsap.utils.wrap(0, 360, 370);  // 10
gsap.utils.wrap(0, 360, -10);   // 350

let wrapFn = gsap.utils.wrap(0, 360);
wrapFn(370); // 10

wrapYoyo(min, max, value?)

Wraps value in range with a yoyo (bounces at ends). Use for back-and-forth within a range. Omit value to get a function: wrapYoyo(min, max)(value).

gsap.utils.wrapYoyo(0, 100, 150); // 50 (bounces back)

let wrapY = gsap.utils.wrapYoyo(0, 100);
wrapY(150); // 50

Best practices

• ✅ Omit the value argument to get a reusable function when the same range/config is used many times (e.g. scroll handler, tween callback): let mapFn = gsap.utils.mapRange(0, 1, 0, 360); mapFn(progress).
• ✅ Use snap for grid-aligned or step-based values; use toArray when GSAP or your code needs a real array from a selector or NodeList.
• ✅ Use gsap.utils.selector(scope) in components so selectors are scoped to a container or ref.

Do Not

• ❌ Assume mapRange / normalize handle units; they work on numbers. Use getUnit / unitize when units matter.
• ❌ Override or rely on undocumented behavior; stick to the documented API.

Learn More

https://gsap.com/docs/v3/HelperFunctions

Codex Web Motion Overlay

The upstream GreenSock official skill content above is the primary GSAP guidance. This local overlay adds Codex-specific progressive-disclosure resources, static audit scripts, evals, and portable source metadata. Keep GSAP API behavior aligned with GreenSock's official skill and docs; use this overlay for validation, local boundaries, and report shape.

Local Boundaries

• Use plain JavaScript helpers when GSAP is not already part of the animation stack.
• Use gsap-core when helper values feed tweens.
• Use gsap-scrolltrigger when helpers map scroll progress.

Local Workflow

1. Identify whether the helper should return a reusable function or immediate value.
2. Keep unit handling explicit.
3. Scope selector helpers in component code.
4. Test boundary inputs and cyclic values.

Local Gotchas

• mapRange and normalize operate on numbers, not unit strings.
• Omitting the final value returns a reusable function; this is often the intended pattern.
• selector(scope) prevents cross-component targeting mistakes.

Bundled Resources

• references/official-source.md - Official GreenSock utils skill source. Use this to verify copied upstream helper guidance.
• references/numeric-mapping.md - Numeric mapping and snapping reference. Use this for clamp, mapRange, normalize, interpolate, snap, wrap, and wrapYoyo.
• references/selectors-and-units.md - Selector scoping and unit helper notes. Use this for toArray, selector, unitize, getUnit, and function-based values.
• references/function-composition-recipes.md - gsap.utils function composition recipes. Read when clamp, mapRange, normalize, interpolate, snap, pipe, unitize, wrap, or selector utilities feed animation values.
• references/random-determinism-testing.md - Randomness, wrapping, and deterministic testing. Read when random, shuffle, wrap, wrapYoyo, or function-based values affect visual output.
• references/index.md - Complete reference inventory and routing summary.
• references/source-ledger.md - Portable source list and copy policy.
• references/provenance.json - Machine-readable provenance and local-resource metadata.
• scripts/audit.mjs - Self-contained Codex audit CLI with domain-specific GSAP rules.
• assets/templates/gsap-utils-audit-report.md - GSAP audit response template.
• assets/templates/gsap-utils-review-checklist.md - GSAP manual review checklist.
• assets/examples/gsap-utils-starter.js - Minimal starter fixture/example.
• evals/trigger-queries.json - Trigger/near-miss eval set.
• evals/evals.json - Task-quality evals with assertions.

Audit CLI

node scripts/audit.mjs doctor --root . --format json
node scripts/audit.mjs scan --root . --format markdown
node scripts/audit.mjs scan --root . --format json --output gsap-utils-audit.json

Treat script findings as leads. Verify every finding against current code before changing behavior or reporting it as valid.