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
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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
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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().
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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().)
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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.
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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.
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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