1.0.0 • Public • Published

Declarative z-indexes (declarative-z-indexes)

Prevent z-index conflicts by generating them from declarative constraints

Have you ever struggled with exponential z-index wars? Have you ever changed a z-index only to find that you now need to change several others? Then declarative z-indexes are for you.

Instead of writing each z-index separately, you write out all of the different relationships between your z-index layers. Then, suitable z-indexes are generated for each of the layers. Easy as pie!

Table of Contents


The idea for this library originally came from UIKit's Auto Layout constraints.


Install using npm:

npm install declarative-z-indexes


First, create a solver using the exported LayerSolver class

const solver = new LayerSolver();

Then, create some layers to be solved for

const body = solver.addLayer("body");
const header = solver.addLayer("header");
const modal = solver.addLayer("modal");

Add constraints between your layers


And finally, generate your z-indexes!

const solution = solver.solve(); // {body: 1, header: 2, modal: 3}

Note: Don't depend on the actual z-index values that are produced! The generated z-indexes will always satisfy the constraints but the literal values might change in future versions of this library. For instance, in the future solver.solve() might return something else like {body: 100, header: 150, modal: 200} if the generating algorithm is changed.

Use the generated z-indexes in inline styles

  <header style={{ position: "absolute", zIndex: solution.header }}>
  <article style={{ zIndex: solution.body }}>



LayerSolver is the default export of declarative-z-indexes.

  • addLayer(name: string): Layer
    The addLayer method returns a new dynamic layer to be solved for. The same name cannot be reused for multiple layers.

  • addStaticLayer(name: string, index: number): Layer
    The addStaticLayer method returns a new static layer. Static layers have a static z-index that will be used when solving the constraints for the dynamic layers.

    Example uses cases for static layers might be external library z-indexes that cannot be modified.

    const solver = new LayerSolver();
    const modal = solver.addStaticLayer('bootstrapModal', 1000);
    const modalDecoration = solver.addLayer('modalDecoration');
    solver.solve(); // {bootstrapModal: 1000, modalDecoration: 1001}

    (Note again: the resulting value of bootstrapModal will always be 1000, but don't depend on modalDecoration being 1001! Its value will be above 1000 but the literal value might change in a future version of the library)

  • solve(): {[layer: string]: number}
    The solve method solves the current constraints on the dynamic layers and returns a map-like object from each layer's name to the generated z-index value.

    solve is idempotent: every time you call it, solve generates a brand new solution based on the constraints currently stored in the solver. It's safe to call solve multiple times and even add new constraints between calls without affecting past solutions.


A Layer is the object that is used to specify constraints in the system. It is returned from a LayerSolver's addLayer and addStaticLayer methods.

  • isAbove(layer: Layer)
    The isAbove method adds a constraint that the current layer should be above the passed in layer.

  • isBelow(layer: Layer)
    The isBelow method adds a constraint that the current layer should be below the passed in layer.


The initial design and API of this library is still being created! Once that is done, we'll start taking contributions. Until then, hold tight!





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