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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Support proposed ES Rest/Spread properties","articleBody":"es7 proposal : https://github.com/sebmarkbage/ecmascript-rest-spread\n## Spread properties\n### Typing\n\nIn my opinion the goal of this method is to be able to duplicate an object and changing some props, so I think it's particularly important in this case to not check duplicate property declaration : \n\n``` typescript\nvar obj = { x: 1, y: 2};\nvar obj1 = {...obj, z: 3, y: 4}; // not an error\n```\n\nI have a very naive [type check algorithm](https://github.com/fdecampredon/jsx-typescript/blob/3c692cbb80622b74d1b308b3c5dcab6b993b4111/src/compiler/checker.ts#L5665-L5671) for a similar feature (`JSXSpreadAttribute`) in my little `jsx-typescript` fork: I just copy the properties of the _spread object_ in the properties table when I encounter a spread object, and override those property if I encounter a declaration with a similar name.\n### Emitting\n\n[jstransform](https://github.com/facebook/jstransform/) use `Object.assign`, [babel](https://babeljs.io/) introduce a shim: \n\n``` javascript\nvar _extends = Object.assign || function (target) { for (var i = 1; i \u003c arguments.length; i++) { var source = arguments[i]; for (var key in source) { if (Object.prototype.hasOwnProperty.call(source, key)) { target[key] = source[key]; } } } return target; };\n```\n\nWe could either force the presence of `assign` function on `ObjectConstructor` interface, or provide a similar function (with a different name).\n\nI think that the optimal solution would be to not emit any helper in `es6` target (or if `Object.assign` is defined), and to emit an helper function for `es5`, `es3`.\n\n``` javascript\nvar obj = { x: 1, y: 2};\nvar obj1 = {...obj, z: 3};\n\n/// ES6 emit\nvar obj = {x: 1, y: 2};\nvar obj1= Object.assign({}, obj, { z: 3 });\n\n//ES3 emit\nvar __assign = function (target) { \n    for (var i = 1; i \u003c arguments.length; i++) { \n        var source = arguments[i]; \n        for (var key in source) { \n            if (Object.prototype.hasOwnProperty.call(source, key)) { \n                target[key] = source[key];\n            } \n        } \n    } \n    return target; \n};\n\nvar obj = {x: 1, y: 2};\nvar obj1= __assign({}, obj, { z: 3 });\n```\n## Rest properties\n### Typing\n\nFor simple object the new type is a subtype of the assignation that does not contains properties that has been captured before the rest properties : \n\n``` typescript\nvar obj = {x:1, y: 1, z: 1};\nvar {z, ...obj1} = obj;\nobj1// {x: number; y:number};\n```\n\nIf the destructuring assignment has an index declaration, the result has also a similar index declaration: \n\n``` typescript\nvar obj: { [string: string]: string };\nvar {[excludedId], ...obj1} = obj;\nobj1// { [string: string]: string };\n```\n\nnew/call declarations are obviously not captured:\n\n``` typescript\nvar obj: { (): void; property: string};\nvar { ...obj1} = obj;\nobj1// { property: string };\n```\n### Emitting\n\nIt is not possible to emit _rest properties_ without an helper function, this one is from babel: \n\n``` typescript\nvar obj = {x:1, y: 1, z: 1};\nvar {z, ...obj1} = obj;\n```\n\n``` javascript\nvar __objectWithoutProperties = function(obj, keys) {\n    var target = {};\n    for (var i in obj) {\n        if (keys.indexOf(i) \u003e= 0) continue;\n        if (!Object.prototype.hasOwnProperty.call(obj, i)) continue;\n        target[i] = obj[i];\n    }\n    return target;\n};\n\nvar obj = {x:1, y: 1, z: 1};\nvar z = obj.z;\nvar obj1 = __objectWithoutProperties(obj, [\"z\"]);\n```\n\n_Edit: added some little typing/emitting example_\n","author":{"url":"https://github.com/fdecampredon","@type":"Person","name":"fdecampredon"},"datePublished":"2015-02-21T21:31:32.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":96},"url":"https://github.com/2103/TypeScript/issues/2103"}