CLI stands for command-line interface and REPL stands for Read Eval Print and Loop. Almost every programming language/environment or even framework provides REPL to play around with the features available.
In this article, we will be using NodeJs REPL to get started with NodeJs.
Lets Start
node
You will get a screen something like
Autocomplete
NodeJs REPL allows autocompleting out of the box.
hit tab (2) times
You will see the huge list of the modules available on NodeJs. Something similar to this
>
AbortController AbortSignal AggregateError Array ArrayBuffer
Atomics BigInt BigInt64Array BigUint64Array Boolean
Buffer DataView Date Error EvalError
Event EventTarget FinalizationRegistry Float32Array Float64Array
Function Infinity Int16Array Int32Array Int8Array
Intl JSON Map Math MessageChannel
MessageEvent MessagePort NaN Number Object
Promise Proxy RangeError ReferenceError Reflect
RegExp Set SharedArrayBuffer String Symbol
SyntaxError TextDecoder TextEncoder TypeError URIError
URL URLSearchParams Uint16Array Uint32Array Uint8Array
Uint8ClampedArray WeakMap WeakRef WeakSet WebAssembly
_ _error assert async_hooks atob
btoa buffer child_process clearImmediate clearInterval
clearTimeout cluster console constants crypto
decodeURI decodeURIComponent dgram diagnostics_channel dns
domain encodeURI encodeURIComponent escape eval
events fs global globalThis http
http2 https inspector isFinite isNaN
module net os parseFloat parseInt
path perf_hooks performance process punycode
querystring queueMicrotask readline repl require
setImmediate setInterval setTimeout stream string_decoder
sys timers tls trace_events tty
undefined unescape url util v8
vm wasi worker_threads zlib
__proto__ hasOwnProperty isPrototypeOf propertyIsEnumerable toLocaleString
toString valueOf
constructor
global
We can find all the properties of global object with
global. +(tab)
List will look similar to
global.__proto__ global.hasOwnProperty global.isPrototypeOf global.propertyIsEnumerable
global.toLocaleString global.toString global.valueOf
global.constructor
global.AbortController global.AbortSignal global.AggregateError global.Array
global.ArrayBuffer global.Atomics global.BigInt global.BigInt64Array
global.BigUint64Array global.Boolean global.Buffer global.DataView
global.Date global.Error global.EvalError global.Event
global.EventTarget global.FinalizationRegistry global.Float32Array global.Float64Array
global.Function global.Infinity global.Int16Array global.Int32Array
global.Int8Array global.Intl global.JSON global.Map
global.Math global.MessageChannel global.MessageEvent global.MessagePort
global.NaN global.Number global.Object global.Promise
global.Proxy global.RangeError global.ReferenceError global.Reflect
global.RegExp global.Set global.SharedArrayBuffer global.String
global.Symbol global.SyntaxError global.TextDecoder global.TextEncoder
global.TypeError global.URIError global.URL global.URLSearchParams
global.Uint16Array global.Uint32Array global.Uint8Array global.Uint8ClampedArray
global.WeakMap global.WeakRef global.WeakSet global.WebAssembly
global._ global._error global.assert global.async_hooks
global.atob global.btoa global.buffer global.child_process
global.clearImmediate global.clearInterval global.clearTimeout global.cluster
global.console global.constants global.crypto global.decodeURI
global.decodeURIComponent global.dgram global.diagnostics_channel global.dns
global.domain global.encodeURI global.encodeURIComponent global.escape
global.eval global.events global.fs global.global
global.globalThis global.http global.http2 global.https
global.inspector global.isFinite global.isNaN global.module
global.net global.os global.parseFloat global.parseInt
global.path global.perf_hooks global.performance global.process
global.punycode global.querystring global.queueMicrotask global.readline
global.repl global.require global.setImmediate global.setInterval
global.setTimeout global.stream global.string_decoder global.sys
global.timers global.tls global.trace_events global.tty
global.undefined global.unescape global.url global.util
global.v8 global.vm global.wasi global.worker_threads
global.zlib
All of these are the top-level objects and modules available on the global object.
Remember: Some of them can not be used on the code you will write.
You can always do console.log(global) to see what you can use on your codebase.
<ref *1> Object [global] {
global: [Circular *1],
clearInterval: [Function: clearInterval],
clearTimeout: [Function: clearTimeout],
setInterval: [Function: setInterval],
setTimeout: [Function: setTimeout] {
[Symbol(nodejs.util.promisify.custom)]: [Getter]
},
queueMicrotask: [Function: queueMicrotask],
clearImmediate: [Function: clearImmediate],
setImmediate: [Function: setImmediate] {
[Symbol(nodejs.util.promisify.custom)]: [Getter]
}
}
Autocomplete works for any object.
Array
Let's create an empty array to see what functions are available on the array object.
const arr = [];
// And
arr.+(tab)
You can find a list of something like
arr.__defineGetter__ arr.__defineSetter__ arr.__lookupGetter__ arr.__lookupSetter__
arr.__proto__ arr.hasOwnProperty arr.isPrototypeOf arr.propertyIsEnumerable
arr.valueOf
arr.concat arr.constructor arr.copyWithin arr.entries
arr.every arr.fill arr.filter arr.find
arr.findIndex arr.flat arr.flatMap arr.forEach
arr.includes arr.indexOf arr.join arr.keys
arr.lastIndexOf arr.map arr.pop arr.push
arr.reduce arr.reduceRight arr.reverse arr.shift
arr.slice arr.some arr.sort arr.splice
arr.toLocaleString arr.toString arr.unshift arr.values
arr.length
You can also have some starting characters autocomplete
arr.co + (tab)
The output will look something like
arr.concat arr.constructor arr.copyWithin
Saving previous value on REPL
You can always create a variable and store the value on it. If you don't want to create a new variable each time you do some calculation, you can use _ to store the previous value.
For example, lets create a random number with Math.random().
Math.random()
And then
_
You will get previous output stored on _.
You can also use this value for further calculation.
_ * 10
All together ( Values can be different on yours)
> Math.random()
0.5641577091577177
> _
0.5641577091577177
> _ * 10
5.641577091577177
> _
5.641577091577177
>
Special commands
You can get special command with . (period sign) + tab.
. + (tab)
A list of special commands will be listed like:
break clear editor exit help load save
You can use any of these commands preceding with .. In our case since we are wrapping this article here, we will be using .exit.
.exit
Thank you!!!