Basic API cognition of node learning

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process.nextTick()

• node Each time a complete trip is made in the event cycle , We all call it a Tick tock .
• When a function is passed to process.nextTick() when , Indicates that the engine is at the end of the current operation （ Before the next event cycle starts ） Call this function when .( Be similar to vue Of $nextTick)

process.nextTick(() => {
    //  What needs to be done 
})
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The event loop is processing the current function code .

When the operation ends ,js The engine will run and pass it to nextTick All functions called .

This way, , You can tell js The engine needs to do something as soon as possible .

and setTimeout The function is executed at the end of the next tick , Than using nextTick() Much later .

When you want to ensure that the code has been executed in the next event loop iteration , Then use  nextTick().

setImmediate()

• When you want to asynchronously （ But as soon as possible ） When executing some code , One option is to use Node.js Provided  setImmediate()  function
• As setImmediate() Any function passed in by the parameter is a callback executed in the next iteration of the event loop .
• Pass to  process.nextTick()  In the current iteration of the event loop （ After the current operation ） Be performed . This means that it will always be  setTimeout  and  setImmediate  Before execution .
• setTimeout  and  setImmediate All belong to macro tasks .
• setImmediate()（ It is equivalent to using  setTimeout(() => {}, 0)）

setTimeout and setInterval

• setTimeout  Will delay the function n Seconds later .

• setTimeout  It will return to the timer id. It is not normally used , But you can save this id, And clear it when the scheduled function is to be deleted

• setInterval  Every time n MS starts a function , and There is no need to consider when the function completes execution . In this way, it may cause , A longer execution will overlap with the next execution . To avoid that , You can schedule the recursive... To be called when the callback function completes setTimeout