Lu Xun said : Only those who have read excellent library source code , To be worthy of a real warrior .

compact

Create a new array , Contains all the non false elements in the original array . for example false, null,0, “”, undefined, and NaN They're all supposed to be “ False value ”.

Note that the above description does not include [],{} Because in js in , The two values are implicitly converted to true. In other words, the function doesn't filter these two values .

Official code :

export function compact(array){
let resIndex = 0;
const result = []
if(array == null){ // Will be able to undefined Get rid of it because undefined == null by true
return result
}
for(const value of array){
if(value){
result[resIndex++] = value
}
}
return result
}

Personal understanding of code :

export function compact(array){
let resIndex = 0;
const result = []
if(array == null){ // Will be able to undefined Get rid of it because undefined == null by true
return result
}
result = array.filter(v=>Boolean(v))
return result
}

Direct use of filter Traversal , utilize boolean, To convert elements to true or false .

concat

Create a new array , take array With any array or Values are linked together .

var array = [1];
var other = _.concat(array, 2, [3], [[4]]); console.log(other);
// => [1, 2, 3, [4]] console.log(array);
// => [1]

relatively speaking ,concat Function depends on a few more tool functions .

  1. arrayPush Array adding method
  2. copyArray Copy array elements
  3. baseFlatten Flat hierarchical array
export function concat(){

let length = arguments.length; //  Get the number of parameters 
if (!length) {
return [];
}
let args = Array(length - 1); // Take the length of the parameter other than the first one
let array = arguments[0]; // Take the first item of the array
let index = length;
while (index--) {
args[index - 1] = arguments[index];
}
console.log(args); // Take the first parameter, which is the target array , As -1 Item added as array
// Determine whether a parameter is an array , No, just convert it to an array , If it is an array, copy an array , Reuse arrayPush Method , Push the parameters of each item into the array .
return arrayPush(Array.isArray(array) ? copyArray(array) : [array], baseFlatten(args, 1));
}

copyArray

Copy an array , This operation does not affect the original array .

Parameters explain
soure Original array parameters
array Result array
export function copyArray(source,array){
let index = -1;
let length = source.length;
array || (array = Array(length));
while(++index < length){
array[index] = source[index]
}
return array
}

baseFlatten

This method is mainly used for flat array operation

export function baseFlatten(array, depth, predicate, isStrict, result) {
let index = -1;
let length = array.length;
predicate || (predicate = isFlattenable); // isFlattenable Determine if it's an array
result || (result = []);
while (++index < length) {
let value = array[index];
console.log(value);
if (depth > 0 && predicate(value)) { // If the level is greater than 0 And the item is an array
if (depth > 1) { // If the level of recursion is greater than 1 In this case, we will continue to solve the problem recursively
baseFlatten(value, depth - 1, predicate, isStrict, result);
} else { // If recursion is required, the level of recursion is 1 The situation of , All items are added to the target array
arrayPush(result, value);
}
} else if (!isStrict) {
result[result.length] = value;
}
}
return result;
}
isFlattenable(value){
return Array.isArray(value)
}

divergent thinking , As long as the function is passed through the depth Variable , To control the level of screening , So I want to flatten all arrays , How to operate it ?

function flattern(arr) {
return arr.reduce((cur, next) => cur.concat(Array.isArray(next) ? flattern(next) : next), []);
}

arrayPush

Add elements into the original array , Will change the original array structure , similar push Method

	 let index = -1;
let length = values.length;
let offset = array.length;
while (++index < length) {
array[index + offset] = values[index];
}
return array;

summary

  1. ++index and index++ The difference ,++i That is to add before use ,i++ That is to use it first and add it later . In front of ++ The subscript will not cross the boundary , After ++ The subscript crossing the line .
  2. lodash library The operation array generally does not affect the original array .

read lodash Source code tour array method -compact and concat More articles about

  1. Read with your hands Mybatis Source code ( 3、 ... and ) Cache

    Preface Hello everyone , This article is MyBatis The last article in the series , The first two articles : Read with your hands Mybatis Source code ( One ) Structure   and   Read with your hands Mybatis Source code ( Two ) Execution , It mainly explains MyBatis How is it? ...

  2. lodash Source analysis of the array difference set

    The shabby and poor appearance of the outside world , It can balance my inner world . -- Calvino < smoke and clouds > This article is for reading lodash Chapter 17 of the source code , Subsequent articles will be updated to this repository , welcome star:pocket-lodas ...

  3. Read with your hands Mybatis Source code ( One ) Structure

    Preface Today we will share our common persistence layer framework ——MyBatis Working principle and source code analysis of , The follow-up will focus on Mybatis Framework to do some more in-depth explanation , After that, the content will be placed in the official account menu bar. : In the serial …- In frame analysis , Welcome to explore ! ...

  4. Read with your hands Mybatis Source code ( Two ) Execution

    Preface The last article mentioned MyBatis How to build configuration class , Also said that the MyBatis In the process of operation, it is mainly divided into two stages , The first is to build , The second is implementation , So this article will take you to understand MyBatis How to start from the end of the build , To carry out ...

  5. From the source point of view finish() Method execution flow

    1. finish() Method Overview Let's look at it first finish The definition of the nonparametric version of a method : /** * Call this when your activity is done and should be c ...

  6. lodash Data type of source code analysis

    All the sadness , There is always a trace of joy left behind , All the regrets , There will always be a perfect corner left , I am in the deep sea of iceberg , Looking for the gap of hope , But when I woke up , A glimpse of the beautiful sunshine ! -- A few meters This article is for reading lodash Source code Chapter 18 , Subsequent articles will be updated to ...

  7. read lodash Source code from slice Sparse array and dense array

    Despicable is the pass of the despicable , Noble is the epitaph of noble . -- The north island < answer > Look at the North Island. It's from these two lines , The noble is dead , Only despicable people are left to roam the world . This article is for reading lodash The first chapter of source code , Subsequent articles will be updated to this warehouse ...

  8. lodash Source code analysis compact Traversal in

    When I was a child , Nostalgia is a small stamp , I'm here , Mother is over there . When I grow up , Nostalgia is a narrow ticket , I'm here , The bride is over there . Later on , Nostalgia is a short grave , I'm outside , Mother is inside . And now , Homesickness is a shallow bay ...

  9. lodash Source code analysis Hash cache

    In the warm Pavilion of little dream , I collect the misty rain of the whole season for you . -- Love < Linghe > This article is for reading lodash The fourth source code , Subsequent articles will be updated to this repository , welcome star:pocket-lodash gitbo ...

  10. lodash Source code analysis List cache

    Yesterday I walked along the river bank / Stroll to / Where the reeds bend to drink By the way, chimney / Write me a long letter in the sky It's a bit sloppy / And my heart / So bright as the candle in front of your window / A little bit ambiguous / be certainly unavoidable / Because of the wind -- Love < Because of the wind & ...

Random recommendation

  1. Gephi visualization ( One )—— Use Gephi Toolkit establish Gephi application

    stay Prefuse I've been up and down for a while , Found it amiable , Easy to use . But it's always on gephi, When importing data and running again , Always in the heart secretly praise gephi The most gorgeous , No match , Of course ,gephi It also has its own shortcomings , however ge ...

  2. Android Mobile phone guard --home Interface layout

    In this paper, the implementation of when from splash Interface into the hone Interface time , Produce a gradual fade in animation effect , stay onCreate A method is invoked in initAnimation(), The code is as follows : /** * Add fade in animation */ pri ...

  3. [Python] solve python The chain extend The technique of

    as everyone knows python Medium list Yes. extend Of , function The aim is to combine the two list Merge into one . for example [1,2,3].extend([4,5,6])=[1,2,3,4,5,6] If there is one list Of list, ...

  4. C# Read web source code

    #region 1. Read Web source code + static string ReadHtml(string urlStr,int type) /// <summary> /// Read Web source code + ...

  5. SQL General query details

    One . Cross connect (cross join) Cross connect (cross join): There are two kinds of , Explicit and implicit , No on Clause , It returns the product of two tables , It's also called Cartesian product . for example : The following statement 1 And statement 2 The result is the same . sentence 1: implicit ...

  6. Problems in audio software development debug Methods and tools

    This article was originally written by the author . Such as reprint , Please indicate the source . thank you ! Audio software development is the same as other software development , All need to be debugged . Audio software debugging has the same place with other software debugging methods , There are different places , At the same time, some special tools are needed for debugging , With these methods ...

  7. BASIC-3 Alphabetic figure loop character string

      Based on practice Alphabetic figure   The time limit :1.0s   Memory limit :256.0MB        Problem description The use of letters can form some beautiful graphics , Here is an example : ABCDEFG BABCDEF CBABCD ...

  8. vim The simple use of and some commonly used commands

    For the first time vi, There are a few points to be reminded of :1. use vi After opening the file , Is in 「 Command line mode (command mode)」, You want to switch to 「 Insertion mode (Insert mode)」 To be able to input text . Switching method : stay 「 Command line mode ...

  9. The development of enterprise firewall iptables

    1.1 Principles of security optimal allocation in Enterprises Try not to configure the external network for the server ip , It can be forwarded by proxy or mapped by firewall . Concurrency is not particularly large, there are extranets ip, You can start the firewall service . Large concurrent cases , Can't open iptables, Affect performance , ...

  10. spring( Four ) Manual integration web project (SSH)

    It's clear spring Of IOC and AOP, The last one is integration SSH Frame the , recorded , It should be used in the future . --WH One .web How to use in a project spring? When tomcat Startup time , It should be loaded spring Configuration of ...