Js Basic knowledge notes

    1 var a = b = 1; infunctionWrite to causes global leakage of variablesb/ / hang onwindowUpper 2 Fibonacci sequence // 1 1 2 3 5 8 13 21 //n1   n2   n3
            //     n1   n2   n3
            //         n1   n2   n3
            //             n1   n2   n3
            let n1 = 1;
            let n2 = 1;
            let n3;
            let n = Number(window.prompt('Please enter n valid value'))
            if (n <= 0) {
                    alert('undifiend')}else {
                    if (n <= 2) {
                        n1 = n2 = 1
                    }
                              for (let i = 0; i < n; i++) {
                            n3 = n1 + n2;
                            n1 = n2;
                            n2 = n3;
                     }
                     console.log(n3)
                }


    3Function expressions (anonymous function expressions/function literals)let test = function test1(){
                    let a = 1,b = 2;
                    cosole.log(a, b)
                    test1() / / closures
            }
            test1() // is not defined is ignored in external calls

    4 funtion test(a,b){
                    cosole.log(test.length)  // The length of the parameter is 2
                    cosole.log(arguments.length)  // The argument length is 3
            }
      test(1.2.3)



    5If an argument is passed a value, the parameter can change its value. If an argument is not passed a value, the parameter can change its valueundefined
    var a =1
        function test(a,b){
            console.log(a)  
            console.log(b)
            a = 2; 
            b = 22;
            / / a and the arguments [0]
            console.log(a, arguments[0])  
            console.log(b, arguments[1])  
        }
        test(a)
        console.log(a)
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