Lodash Js Part 2(Chaining and has method)

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Lodash Js Part 2(Chaining and has method)

2019年11月29日
技術情報

Today I will talk about chaining functions and has method.

Chaining

Without Chaining

var data1 = [10, 15, 20, 25, 15];

var data2 = _.filter(data1, function(item){ return item % 10 === 5 });
// data2 now contains [15, 25, 15]

var data3 = _.uniq(data2);
// data3 now contains [15, 25]

var data4 = _.map(data3, function(item){ return item + 1 });
// data4 now contains [16, 26]

var data1 = [10, 15, 20, 25, 15];

var data2 = _.filter(data1, function(item){ return item % 10 === 5 });

// data2 now contains [15, 25, 15]

var data3 = _.uniq(data2);

// data3 now contains [15, 25]

var data4 = _.map(data3, function(item){ return item + 1 });

// data4 now contains [16, 26]

With Chaining

var data1 = [10, 15, 20, 25, 15];

var data4 = _(data1)
    .filter(function(item){ return item % 10 === 5 })
    .uniq()
    .map(function(item){ return item + 1 })
    .value();
// data4 now contains [16, 26]

var data1 = [10, 15, 20, 25, 15];

var data4 = _(data1)

.filter(function(item){ return item % 10 === 5 })

.uniq()

.map(function(item){ return item + 1 })

.value();

// data4 now contains [16, 26]

The chaining is more efficient.
no intermediate results are created.

Slight Changes for `Explicit Chain` & `Implicit Chain`

Explicit chaining

Still need to unwrap the result with .value().

var data = [1, 5, 10, 15, 5, 10, 1, 20];

var unqSum = _.chain(data)
   .uniq()
   .sum()       
   .value();   
result is 51

var data = [1, 5, 10, 15, 5, 10, 1, 20];

var unqSum = _.chain(data)

.uniq()

.sum()

.value();

result is 51

Implicit chaining

The “unwrapping” of the single value is implied. (there is no need to call .value().)

var data = [1, 5, 10, 15, 5, 10, 1, 20];

var unqSum = _(data)
    .uniq()
    .sum();  
    
    //result is 51

var data = [1, 5, 10, 15, 5, 10, 1, 20];

var unqSum = _(data)

.uniq()

.sum();

//result is 51

has

Determine if an object has (or contains) a key.

var obj = {
  data1: 2,
  data2: 3,
  data3: {
    data3_1:40,
    data3_2:{
      data3_2_1:500
    }
  }
};

var res1 = _.has(obj, "data1");          // true
var res2 = _.has(obj, "data1.data2");        // false
var res3 = _.has(obj, "data3");          // true
var res4 = _.has(obj, "data3.data3_2");       // true
var res5 = _.has(obj, "data3.res3_2_1");      // false
var res6 = _.has(obj, "data3.data3_1.data3_2_1");   // false
var res7 = _.has(obj, "data3.data3_2.data3_2_1");   // true

var obj = {

data1: 2,

data2: 3,

data3: {

data3_1:40,

data3_2:{

data3_2_1:500

}

};

var res1 = _.has(obj, "data1"); // true

var res2 = _.has(obj, "data1.data2"); // false

var res3 = _.has(obj, "data3"); // true

var res4 = _.has(obj, "data3.data3_2"); // true

var res5 = _.has(obj, "data3.res3_2_1"); // false

var res6 = _.has(obj, "data3.data3_1.data3_2_1"); // false

var res7 = _.has(obj, "data3.data3_2.data3_2_1"); // true

Arrays can be used to split up parts.

var res8 = _.has(obj, ["data1", "data2"]);   // false, same as res2
var res9 = _.has(obj, ["data3", "data3_2"]);  // true, same as res4

1 2	var res8 = _.has(obj, ["data1", "data2"]); // false, same as res2 var res9 = _.has(obj, ["data3", "data3_2"]); // true, same as res4

By Yuuma

yuuma at 2019年11月29日 11:00:07

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