Add 6 new snippets

snippets/callOrReturn.md

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+---
+title: Call or return
+tags: function
+expertise: beginner
+firstSeen: 2022-04-04T05:00:00-04:00
+---
+
+Calls the argument if it's a function, otherwise returns it.
+
+- Use the `typeof` operator to check if the given argument is a function.
+- If it is, use the spread operator (`...`) to call it with the rest of the given arguments. Otherwise, return it.
+
+```js
+const callOrReturn = (fn, ...args) =>
+  typeof fn === 'function' ? fn(...args) : fn;
+```
+
+```js
+callOrReturn(x => x + 1, 1); // 2
+callOrReturn(1, 1); // 1
+```

snippets/commonKeys.md

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+---
+title: Common keys
+tags: object
+expertise: intermediate
+firstSeen: 2022-04-23T05:00:00-04:00
+---
+
+Finds the common keys between two objects.
+
+- Use `Object.keys()` to get the keys of the first object.
+- Use `Object.prototype.hasOwnProperty()` to check if the second object has a key that's in the first object.
+- Use `Array.prototype.filter()` to filter out keys that aren't in both objects.
+
+```js
+const commonKeys = (obj1, obj2) =>
+  Object.keys(obj1).filter(key => obj2.hasOwnProperty(key));
+```
+
+```js
+commonKeys({ a: 1, b: 2 }, { a: 2, c: 1 }); // ['a']
+```

snippets/compactJoin.md

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+---
+title: Compact and join array
+tags: array
+expertise: intermediate
+firstSeen: 2022-04-08T05:00:00-04:00
+---
+
+Removes falsy values from an array and combines the remaining values into a string.
+
+- Use `Array.prototype.filter()` to filter out falsy values (`false`, `null`, `0`, `""`, `undefined`, and `NaN`).
+- Use `Array.prototype.join()` to join the remaining values into a string.
+
+```js
+const compactJoin = (arr, delim = ',') => arr.filter(Boolean).join(delim);
+```
+
+```js
+compactJoin(['a', '', 'b', 'c']); // 'a,b,c'
+```

snippets/flags.md

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+---
+title: Array to flags object
+tags: array,object
+expertise: intermediate
+firstSeen: 2022-04-12T05:00:00-04:00
+---
+
+Converts an array of strings into an object mapping to true.
+
+- Use `Array.prototype.reduce()` to convert the array into an object, where each array value is used as a key whose value is set to `true`.
+
+```js
+const flags = arr => arr.reduce((acc, str) => ({...acc, [str]: true }), {});
+```
+
+```js
+flags(['red', 'green']); // { red: true, green: true }
+```

snippets/toggleElement.md

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+---
+title: Toggle element in array
+tags: array
+expertise: beginner
+firstSeen: 2022-04-15T05:00:00-04:00
+---
+
+Removes an element from an array if it's included in the array, or pushes it to the array if it isn't.
+
+- Use `Array.prototype.includes()` to check if the given element is in the array.
+- Use `Array.prototype.filter()` to remove the element if it's in the array.
+- Use the spread operator (`...`) to push the element if it's not in the array.
+
+```js
+const toggleElement = (arr, val) =>
+  arr.includes(val) ? arr.filter(el => el !== val) : [...arr, val];
+
+```
+
+```js
+toggleElement([1, 2, 3], 2); // [1, 3]
+toggleElement([1, 2, 3], 4); // [1, 2, 3, 4]
+```

snippets/unwind.md

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+---
+title: Unwind object
+tags: object
+expertise: intermediate
+firstSeen: 2022-04-18T05:00:00-04:00
+---
+
+Produces an array of objects from an object and one of its array-valued properties.
+
+- Use object destructuring to exclude the key-value pair for the specified `key` from the object.
+- Use `Array.prototype.map()` for the values of the given `key` to create an array of objects.
+- Each object contains the original object's values, except for `key` which is mapped to its individual values.
+
+```js
+const unwind = (key, obj) => {
+  const { [key]: _, ...rest } = obj;
+  return obj[key].map(val => ({ ...rest, [key]: val }));
+};
+```
+
+```js
+unwind('b', { a: true, b: [1, 2] }); // [{ a: true, b: 1 }, { a: true, b: 2 }]
+```