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How I think about default values in JavaScript
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| /** | |
| * How I think about default values in JavaScript | |
| * | |
| * First of all, all these things can fall under the Opinions, Concerns, and Nitpick | |
| * umbrella. The most important thing is just giving thought to the things | |
| * you have opinions about and always reserve the right to be corrected. | |
| * | |
| * My simple rule of thumb is to try to set initial state to whatever the | |
| * eventual state will be for Objects and Arrays. | |
| * | |
| * Strings and numbers default to undefined. | |
| */ | |
| /** | |
| * Describing usage | |
| */ | |
| /** | |
| * Problems defaulting to undefined: | |
| * A lot of times I am just trying to describe how state will be used, | |
| * so setting values that will be used later as `undefined` will give | |
| * future users some understanding of what state might exist | |
| */ | |
| // bad | |
| const initialState = { | |
| // type string | |
| name: undefined, | |
| // type number | |
| age: undefined, | |
| // type array of strings | |
| cars: undefined, | |
| // type deep object {height: string, shoe_size: number} | |
| metaData: undefined | |
| }; | |
| // initialState.cars.map() | |
| // > TypeError: initialState.cars is undefined | |
| // console.log(initialState.metaData.test) | |
| // > TypeError: initialState.metaData is undefined | |
| /** | |
| * Defaulting to `undefined` has been a safer choice overall in my experience, | |
| * because other authors tend to not set object properties befefore usage, or | |
| * they might just not exist on some JSON you get back from a server | |
| */ | |
| /** | |
| * Problems defaulting to null: | |
| * any time you want to use `typeof` you will need to check for two values | |
| * // super error prone | |
| * typeof initialState.name !== "object" && typeof initialState.name === "string" | |
| */ | |
| // Bad | |
| const initialState = { | |
| name: null, | |
| age: null, | |
| cars: null, | |
| metaData: null | |
| }; | |
| // typeof initialState.name | |
| // > "object" | |
| // initialState.cars.map() | |
| // > TypeError: initialState.cars is null | |
| // console.log(initialState.metaData.test) | |
| // > TypeError: initialState.metaData is null | |
| /** | |
| * Problems defaulting to the values type | |
| */ | |
| const initialState = { | |
| age: 0, // is 0 a valid age?, | |
| name: "" // will someone typeof === 'string' and also have to check length? | |
| }; | |
| /** | |
| * My preference, which has in my experience been less error prone. | |
| * The only time I will use null as a default is if some API I am using uses null. | |
| */ | |
| const initialState = { | |
| age: undefined, | |
| name: undefined, | |
| cars: [], | |
| metaData: { height: undefined, shoe_size: undefined } | |
| }; |
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