Easing Map Get Function

Bézier curves can be used to add beautiful effects to CSS transitions and animations. Typing out the full functional notation (e.g. cubic-bezier(0.550, 0.085, 0.680, 0.530)) - for developers writing Sass, is unnecessary.

Bourbon - a popular Sass mixin library, comes pre-packaged with all of the timing functions declared as variables. If you're not using Bourbon, feel free to grab these:

$ease: (
  in-quad:      cubic-bezier(0.550,  0.085, 0.680, 0.530),
  in-cubic:     cubic-bezier(0.550,  0.055, 0.675, 0.190),
  in-quart:     cubic-bezier(0.895,  0.030, 0.685, 0.220),
  in-quint:     cubic-bezier(0.755,  0.050, 0.855, 0.060),
  in-sine:      cubic-bezier(0.470,  0.000, 0.745, 0.715),
  in-expo:      cubic-bezier(0.950,  0.050, 0.795, 0.035),
  in-circ:      cubic-bezier(0.600,  0.040, 0.980, 0.335),
  in-back:      cubic-bezier(0.600, -0.280, 0.735, 0.045),
  out-quad:     cubic-bezier(0.250,  0.460, 0.450, 0.940),
  out-cubic:    cubic-bezier(0.215,  0.610, 0.355, 1.000),
  out-quart:    cubic-bezier(0.165,  0.840, 0.440, 1.000),
  out-quint:    cubic-bezier(0.230,  1.000, 0.320, 1.000),
  out-sine:     cubic-bezier(0.390,  0.575, 0.565, 1.000),
  out-expo:     cubic-bezier(0.190,  1.000, 0.220, 1.000),
  out-circ:     cubic-bezier(0.075,  0.820, 0.165, 1.000),
  out-back:     cubic-bezier(0.175,  0.885, 0.320, 1.275),
  in-out-quad:  cubic-bezier(0.455,  0.030, 0.515, 0.955),
  in-out-cubic: cubic-bezier(0.645,  0.045, 0.355, 1.000),
  in-out-quart: cubic-bezier(0.770,  0.000, 0.175, 1.000),
  in-out-quint: cubic-bezier(0.860,  0.000, 0.070, 1.000),
  in-out-sine:  cubic-bezier(0.445,  0.050, 0.550, 0.950),
  in-out-expo:  cubic-bezier(1.000,  0.000, 0.000, 1.000),
  in-out-circ:  cubic-bezier(0.785,  0.135, 0.150, 0.860),
  in-out-back:  cubic-bezier(0.680, -0.550, 0.265, 1.550)
);

@function ease($key) {
  @if map-has-key($ease, $key) {
    @return map-get($ease, $key);
  }

  @warn "Unkown '#{$key}' in $ease.";
  @return null;
}

Example usage

.example {
  animation: there-and-back 2.5s ease(in-quad) infinite alternate;
}

Demo of all

Thanks to Sean Dempsey (@thatseandempsey).

See the Pen Easing Map Get Function by Sean Dempsey (@seanseansean) on CodePen.

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