An exponent / power function for sassy css

src_pow.scss

///
/// Raises `$number` to the power of `$exponent`.
/// ---
/// @since 1.5.0
/// ---
/// @param {Number} $number
/// @param {Number} $exponent
/// ---
/// @returns {Number} - `$number` raised to the power of `$exponent`
///
@function pow($number, $exponent) {
    // ----- BEGIN ERROR CHECKING ----- //
    @if not type-of($number) == 'number' {
        @error "pow() function expecting `$number` param value to be a number. Was #{$number} (#{type-of($number)}).";
    }

    @if not type-of($exponent) == 'number' {
        @error "pow() function expecting `$exponent` param value to be a number. Was #{$number} (#{type-of($number)}).";
    }
    // ----- END ERROR CHECKING ----- //

    @if $exponent == 0 {
        @return 1;
    }

    // Initialize the value that we will return
    $value: $number;
    // If the provided number is negative, the return value should also be negative
    $preserve-negative: if($value < 0, -1, 1);

    // Multiply when `$exponent` is positive
    @if $exponent > 1 {
        @for $i from 2 through $exponent {
            $value: $value * $number;
        }

        $value: abs($value) * $preserve-negative;
    }

    // Divide when `$exponent` is negative
    @if $exponent < 1 {
        @for $i from 0 through -$exponent {
            $value: $value / $number;
        }

        $value: abs($value) * $preserve-negative;
    }

    @return $value;
}

test_pow.scss

// Tests for pow() (using bootcamp)

@include describe('[pow]') {
    @include describe('when [number] is a positive number') {
        @include describe('and [exponent] is a positive number greater than one') {
            @include it('should return the correct value') {
                $actual: pow(10, 2);

                @include should(expect( $actual ), have-type-of('number'));
                @include should(expect( $actual ), to(be( 100 )));
            }
        }

        @include describe('and [exponent] is one') {
            @include it('should return the correct value') {
                $actual: pow(10, 1);

                @include should(expect( $actual ), have-type-of('number'));
                @include should(expect( $actual ), to(be( 10 )));
            }
        }

        @include describe('and [exponent] is zero') {
            @include it('should return the correct value') {
                $actual: pow(10, 0);

                @include should(expect( $actual ), have-type-of('number'));
                @include should(expect( $actual ), to(be( 1 )));
            }
        }

        @include describe('and [exponent] is negative one') {
            @include it('should return the correct value') {
                $actual: pow(10, -1);

                @include should(expect( $actual ), have-type-of('number'));
                @include should(expect( $actual ), to(be( .1 )));
            }
        }

        @include describe('and [exponent] is a negative number greater than one') {
            @include it('should return the correct value') {
                $actual: pow(10, -2);

                @include should(expect( $actual ), have-type-of('number'));
                @include should(expect( $actual ), to(be( .01 )));
            }
        }
    }

    @include describe('when [number] is a negative number') {
        @include describe('and [exponent] is a positive number greater than one') {
            @include it('should return the correct value') {
                $actual: pow(-10, 2);

                @include should(expect( $actual ), have-type-of('number'));
                @include should(expect( $actual ), to(be( -100 )));
            }
        }

        @include describe('and [exponent] is one') {
            @include it('should return the correct value') {
                $actual: pow(-10, 1);

                @include should(expect( $actual ), have-type-of('number'));
                @include should(expect( $actual ), to(be( -10 )));
            }
        }

        @include describe('and [exponent] is zero') {
            @include it('should return the correct value') {
                $actual: pow(-10, 0);

                @include should(expect( $actual ), have-type-of('number'));
                @include should(expect( $actual ), to(be( 1 )));
            }
        }

        @include describe('and [exponent] is negative one') {
            @include it('should return the correct value') {
                $actual: pow(-10, -1);

                @include should(expect( $actual ), have-type-of('number'));
                @include should(expect( $actual ), to(be( -.1 )));
            }
        }

        @include describe('and [exponent] is a negative number greater than one') {
            @include it('should return the correct value') {
                $actual: pow(-10, -2);

                @include should(expect( $actual ), have-type-of('number'));
                @include should(expect( $actual ), to(be( -.01 )));
            }
        }
    }
}