js: add bare bones js stuff

1 files changed, 75 insertions, 0 deletions

diff --git a/scale.mjs b/scale.mjs
new file mode 100644
index 0000000..61319df
--- /dev/null
+++ b/scale.mjs
@@ -0,0 +1,75 @@
+const ringHandler = {
+    get(target, prop) {
+        return target[prop % target.length] || Reflect.get(...arguments);
+    }
+};
+
+const chromaticScale = new Proxy(
+    ['A', 'A#', 'B', 'C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#'],
+    ringHandler);
+
+function scaleFromIntervals(root, intervals) {
+    const scaleIndex = chromaticScale.indexOf(root);
+    if (scaleIndex < 0) {
+        return undefined;
+    }
+
+    let scale = [root];
+    let steps = 0;
+    let lastBase = root[0];
+    for (let i = 0; i < intervals.length; i++) {
+        steps += intervals[i];
+        const note = chromaticScale[scaleIndex + steps];
+        // don't display two base notes in a row by changing
+        // accidentals.
+        if (note[0] === lastBase) {
+            const nextBase = chromaticScale[scaleIndex + steps + 1][0];
+            scale.push(`${nextBase}b`)
+            lastBase = nextBase[0];
+        } else {
+            scale.push(note);
+            lastBase = note[0];
+        }
+    }
+    return new Proxy(scale, ringHandler);
+}
+
+class Scale {
+    constructor(root, intervals) {
+        this.scale = scaleFromIntervals(root, intervals);
+        return new Proxy(this, {
+            get(target, prop) {
+                return target.scale[prop] || Reflect.get(...arguments);
+            }
+        });
+    }
+
+    get root() {
+        return this[0];
+    }
+
+    get third() {
+        return this[2];
+    }
+
+    get fifth() {
+        return this[4];
+    }
+
+    get length() {
+        console.debug(`get length`, this.scale.length);
+        return this.intervals.length;
+    }
+}
+
+export function MajorScale(root) {
+    console.debug(`MajorScale(${root})`);
+    const intervals = [2, 2, 1, 2, 2, 2];
+    return new Scale(root, intervals);
+}
+
+export function MinorScale(root) {
+    console.debug(`MinorScale(${root})`);
+    const intervals = [2, 1, 2, 2, 1, 2];
+    return new Scale(root, intervals);
+}