Add ability to properly cast a string, number, null to an integer (#990)

front/src/utils/cast-as-integer-or-null.ts

@@ -0,0 +1,58 @@
+export function canBeCastAsIntegerOrNull(
+  probableNumberOrNull: string | undefined | number | null,
+): probableNumberOrNull is number | null {
+  if (probableNumberOrNull === undefined) {
+    return false;
+  }
+
+  if (typeof probableNumberOrNull === 'number') {
+    return Number.isInteger(probableNumberOrNull);
+  }
+
+  if (probableNumberOrNull === null) {
+    return true;
+  }
+
+  if (probableNumberOrNull === '') {
+    return true;
+  }
+
+  if (typeof probableNumberOrNull === 'string') {
+    const stringAsNumber = +probableNumberOrNull;
+
+    if (isNaN(stringAsNumber)) {
+      return false;
+    }
+    if (Number.isInteger(stringAsNumber)) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+export function castAsIntegerOrNull(
+  probableNumberOrNull: string | undefined | number | null,
+): number | null {
+  if (canBeCastAsIntegerOrNull(probableNumberOrNull) === false) {
+    throw new Error('Cannot cast to number or null');
+  }
+
+  if (probableNumberOrNull === null) {
+    return null;
+  }
+
+  if (probableNumberOrNull === '') {
+    return null;
+  }
+
+  if (typeof probableNumberOrNull === 'number') {
+    return probableNumberOrNull;
+  }
+
+  if (typeof probableNumberOrNull === 'string') {
+    return +probableNumberOrNull;
+  }
+
+  return null;
+}