Promise (3.8) Custom (handwritten) Promise — specifies the implementation of multiple callbacks

We need to save all of the callbacks performed in the above then methods: Callacks = [] this. Callacks. Push ({onResolved:onResolved, onRejected:onRejected})

function Promise(executor){
    // Resolve and reject are functions
    
    // Add attributes
    this.PromiseState = "pending";
    this.PromiseResult = null
    
    this.callacks = []
    
    const self = this;
    / / resolve function
    function resolve(data){
        if(self.PromiseState ! = ='pending') return
        // (1) Change the state of the object
        // this.promisestate // This is window because resolve is called directly
        self.PromiseState = 'fulfilled'
        // (2) Set the object result value
        self.PromiseResult = data
        self.callbacks.forEach(item= > {
            item.onResolved(self.PromiseResult)
        })
        
    }
    
    / / reject function
    function reject(data){
       if(self.PromiseState ! = ='pending') return
       // (1) Change the state of the object
        self.PromiseState = 'rejected'
        // (2) Set the object result value
        self.PromiseResult = data
        if(self.callbacks.onRejected){
            self.callbacks.onRejected(self.PromiseResult)
        }
        self.callbacks.forEach(item= > {
            item.onRejected(self.PromiseResult)
        })
    }
    
    // Call the executor function synchronously
    try {
        executor(resolve,reject)
    }catch(e){
        reject(e)
    }
    
}

// Add the then method
Promise.prototype.then = function(onResolved,onRejected){
    if(this.PromiseState == 'fulfilled'){
        onResolved(this.PromiseResult)
    }
    if(this.PromiseState == 'rejected'){
        onRejected(this.PromiseResult)
    }
    
    // Determine pending status
    if(this.PromiseState == 'pending') {// Save the callback function so that it can be called when the state changes
       this.callacks.push({
           onResolved:onResolved,
           onRejected:onRejected
       })
    }
}

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