New javascript features: let, function *, yield, promise

New javascript features: let, function *, yield, promise

I haven't updated my blog for a long time since I went to Baidu. I read the stuff I wrote before. I used to be idle in small companies. The irony is that this time I want to change my job to a small company, I think of writing blogs...

I learned python first after I went to Baidu, and then GG went away. I didn't want to use python anymore, so I tried my best to switch to nodejs.

I like the JS family more and more. I recently read the new features of ECMA6, which actually enhances the vitality of JS. According to a foreign video from ASMJS Daniel, the author of JS created the language in just 10 days.

Therefore, we hope that ECMA can continue to improve.

More nonsense. The following is a dry item. Note that the Code should be executed in node -- harmony and the code should be run in strict mode.

Let is actually the var of the block-level scope declarative variable. Previously, the var keyword of JavaScript is not block-level scope, but function-level.

For example, if arr = [0, 1, 2], we often write a loop for (var I = 0, len = arr. length; I <len; I ++) {}. In fact, after the loop, this I is still accessible 2. In this way, environment variables are easily contaminated.

If let, for (let I = 0, len = arr. length; I

Function * declares the constructor and returns {value: v, done: true_or_false }. The constructor can call next to obtain the next value and construct a random number generator.

Yield and function * are used together. In the constructor function, yield can pause and return the value of the current expression.

For example, function a () {yield 1; yield 2 ;}; var gen = a (); console. log (gen. next (); console. log (gen. next (); console. log (gen. next ();, the result is {value: 1, done: false}, {value: 2, done: false}, {value: undefined, done: true }. after yield 1 in the first line of the constructor a is executed, function a exits and stores the context. When next is executed again, the context of function a is resumed and the next row of B is executed.

Promise, this non-ECMA6 feature, HTML5Rocks has written quite well. It is mainly used to solve the problem of multi-layer nesting. Converts nested callbacks into chained calls.