JavaScript basic data types in
| Data Type Name | Data Type Description |
|---|---|
| Undefined | Only one value, that is undefined , the initial value of the variable declaration. |
| Null | Only one value, i.e. null , indicates a null pointer value is derived value. undefined null |
| String | 16 consists of zero or more Unicode characters |
| Boolean | Only two values, true and false |
| Number | The type used IEEE754 to represent integer and floating point. |
| Object | It is actually a collection of data and functionality in a set of ECMAScript objects. |
| Symbol | ES6 new data type is added, it represents a unique value. |
Wherein the Object type comprising Function , , , . Array Date RegExp
JavaScript built-in objects
| Object Name | Object Description |
|---|---|
| Arguments | Function parameter set |
| Array | Array |
| Boolean | Boolean object |
| Date | Date Object |
| Error | Exception object |
| Function | Function constructor |
| Math | Mathematical objects |
| Number | Numeric objects |
| Object | The base object |
| String | String object |
typeof null Return result 'object'
From the logical point of view, value represents a null object pointer, and therefore a return , is a JavaScript can be understood as an early BUG, and this is now the standard specification. V8 had been corrected and to achieve , but in the end prove feasible. null 'object' typeof null === 'null'
Array And the role of object methods
| Method name | Object Description |
|---|---|
| concat | For connecting two or more array and returns the result, arr1.concat(arr2) |
| join | All the elements of the array into a string, the development of elements separated by delimiters arr1.join(',') |
| pop | Removes and returns the last element in the array arr1.pop() |
| push | Add one or more elements to the end of the array, and returns the new length arr1.push(1) |
| reverse | Reverse the order of elements in the array, arr1.reverse() |
| shift | Removes and returns the first element in the array arr1.shift() |
| slice | Returns the specified element from an existing array |
| sort | Of the elements of the array to sort arr1.sort() |
| splice | Remove elements and add new elements in the array |
The array translated into strings arr1.toString() |
|
Local string array to convert arr1.toLocaleString() |
|
| unshift | Add one or more elements to the beginning of an array arr1.unshift(1) |
| Returns an array of object's original value |
typeof The possible return values
| Types of | Back to Results |
|---|---|
| Undefined | "undefined" |
| Null | "object" |
| Boolean | "boolean" |
| Number | "number" |
| String | "string" |
| Symbol (ECMAScript 6 new) | "symbol" |
| Host object (provided by the environment JS) | Implementation-dependent |
| Function object ([[Call]] implemented in terms of the ECMA-262) | "function" |
| Any other objects | "object" |
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