## _
+ [link](./_ "Link to this entry.")
+ [source](https://github.com/lodash/lodash/blob/4.5.0正式版/lodash.src.js#L1494 "View in source.")
+ [npm](https://www.npmjs.com/package/lodash._ "See the npm package.")
```
_(value)
```
创建一个经 `lodash` 包装后的对象会启用隐式链。返回的数组、集合、方法相互之间能够链式调用。 检索唯一值或返回原始值会自动解除链条并返回计算后的值，否则需要调用 `_#value` 方法解除链(即获得计算结果)。
显式链式调用，在任何情况下需要先用 `_#value` 解除链后，才能使用 `_.chain` 开启。
链式方法是惰性计算的，直到隐式或者显式调用了 `_#value` 才会执行计算。
惰性计算接受几种支持 shortcut fusion 的方法， shortcut fusion 是一种通过合并链式 iteratee 调用从而大大降低迭代的次数以提高执行性能的方式。 部分链有资格 shortcut fusion，如果它至少有超过二百个元素的数组和任何只接受一个参数的 iteratees。 触发的方式是任何一个 shortcut fusion 有了变化。
链式方法支持定制版本，只要 `_#value` 包含或者间接包含在版本中。
除了 lodash 的自身方法，包装后的对象还支持 `Array` 的 `String` 的方法。
支持 `Array` 的方法:
`concat`, `join`, `pop`, `push`, `shift`, `sort`, `splice`, 以及 `unshift`
支持 `String` 的方法:
`replace` 以及 `split`
支持 shortcut fusion 的方法:
`at`, `compact`, `drop`, `dropRight`, `dropWhile`, `filter`, `find`, `findLast`, `head`, `initial`, `last`, `map`, `reject`, `reverse`, `slice`, `tail`, `take`, `takeRight`, `takeRightWhile`, `takeWhile`, 以及 `toArray`
默认不支持 链式调用 的方法:
`add`, `attempt`, `camelCase`, `capitalize`, `ceil`, `clamp`, `clone`, `cloneDeep`, `cloneDeepWith`, `cloneWith`, `deburr`, `endsWith`, `eq`, `escape`, `escapeRegExp`, `every`, `find`, `findIndex`, `findKey`, `findLast`, `findLastIndex`, `findLastKey`, `floor`, `forEach`, `forEachRight`, `forIn`, `forInRight`, `forOwn`, `forOwnRight`, `get`, `gt`, `gte`, `has`, `hasIn`, `head`, `identity`, `includes`, `indexOf`, `inRange`, `invoke`, `isArguments`, `isArray`, `isArrayBuffer`, `isArrayLike`, `isArrayLikeObject`, `isBoolean`, `isBuffer`, `isDate`, `isElement`, `isEmpty`, `isEqual`, `isEqualWith`, `isError`, `isFinite`, `isFunction`, `isInteger`, `isLength`, `isMap`, `isMatch`, `isMatchWith`, `isNaN`, `isNative`, `isNil`, `isNull`, `isNumber`, `isObject`, `isObjectLike`, `isPlainObject`, `isRegExp`, `isSafeInteger`, `isSet`, `isString`, `isUndefined`, `isTypedArray`, `isWeakMap`, `isWeakSet`, `join`, `kebabCase`, `last`, `lastIndexOf`, `lowerCase`, `lowerFirst`, `lt`, `lte`, `max`, `maxBy`, `mean`, `min`, `minBy`, `noConflict`, `noop`, `now`, `pad`, `padEnd`, `padStart`, `parseInt`, `pop`, `random`, `reduce`, `reduceRight`, `repeat`, `result`, `round`, `runInContext`, `sample`, `shift`, `size`, `snakeCase`, `some`, `sortedIndex`, `sortedIndexBy`, `sortedLastIndex`, `sortedLastIndexBy`, `startCase`, `startsWith`, `subtract`, `sum`, `sumBy`, `template`, `times`, `toLower`, `toInteger`, `toLength`, `toNumber`, `toSafeInteger`, `toString`, `toUpper`, `trim`, `trimEnd`, `trimStart`, `truncate`, `unescape`, `uniqueId`, `upperCase`, `upperFirst`, `value`, 以及 `words`
支持 链式调用 的方法:
`after`, `ary`, `assign`, `assignIn`, `assignInWith`, `assignWith`, `at`, `before`, `bind`, `bindAll`, `bindKey`, `castArray`, `chain`, `chunk`, `commit`, `compact`, `concat`, `conforms`, `constant`, `countBy`, `create`, `curry`, `debounce`, `defaults`, `defaultsDeep`, `defer`, `delay`, `difference`, `differenceBy`, `differenceWith`, `drop`, `dropRight`, `dropRightWhile`, `dropWhile`, `fill`, `filter`, `flatten`, `flattenDeep`, `flattenDepth`, `flip`, `flow`, `flowRight`, `fromPairs`, `functions`, `functionsIn`, `groupBy`, `initial`, `intersection`, `intersectionBy`, `intersectionWith`, `invert`, `invertBy`, `invokeMap`, `iteratee`, `keyBy`, `keys`, `keysIn`, `map`, `mapKeys`, `mapValues`, `matches`, `matchesProperty`, `memoize`, `merge`, `mergeWith`, `method`, `methodOf`, `mixin`, `negate`, `nthArg`, `omit`, `omitBy`, `once`, `orderBy`, `over`, `overArgs`, `overEvery`, `overSome`, `partial`, `partialRight`, `partition`, `pick`, `pickBy`, `plant`, `property`, `propertyOf`, `pull`, `pullAll`, `pullAllBy`, `pullAt`, `push`, `range`, `rangeRight`, `rearg`, `reject`, `remove`, `rest`, `reverse`, `sampleSize`, `set`, `setWith`, `shuffle`, `slice`, `sort`, `sortBy`, `splice`, `spread`, `tail`, `take`, `takeRight`, `takeRightWhile`, `takeWhile`, `tap`, `throttle`, `thru`, `toArray`, `toPairs`, `toPairsIn`, `toPath`, `toPlainObject`, `transform`, `unary`, `union`, `unionBy`, `unionWith`, `uniq`, `uniqBy`, `uniqWith`, `unset`, `unshift`, `unzip`, `unzipWith`, `values`, `valuesIn`, `without`, `wrap`, `xor`, `xorBy`, `xorWith`, `zip`, `zipObject`, `zipObjectDeep`, 以及 `zipWith`
### 参数
1. value (\*)
需要被包装为 `lodash` 实例的值.
### 返回值 (Object)
返回 `lodash` 包装后的实例
### 示例
```
function square(n) {
return n * n;
}
var wrapped = _([1, 2, 3]);
// 返回未包装的值
wrapped.reduce(_.add);
// => 6
// 返回链式包装的值
var squares = wrapped.map(square);
_.isArray(squares);
// => false
_.isArray(squares.value());
// => true
```
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