javascript如果比较.shift（）到数组的最后一个值不起作用

Question

I have an array with some nested arrays. I iterate through the array, and nested arrays with .shift(). When the .shift() is equal to the last value in the nested array I iterate through the top level and am logging that with console.log("last member of array"). If the active shift() is not the last value then I log "member of array".

For some reason my if condition to test for the last member of the array isn't working. The weird part is when I log the active shift, and the final value of the array, the log shows they are the same! yet the if statement is not running. Not sure if this is because i'm comparing array with object or what. Any ideas?

for example in log a3ls is the same as b, which means b = a3ls, yet the block in that if statement isn't running!

a3ls: .wePredOpTemps, .pcb_cad,fadeOut,1000
a is: .pcb_cad_cfd,fadeIn,1000,
b is: .wePredOpTemps, .pcb_cad,fadeOut,1000
a[3] is: 
b member

I would think the "b member" should be "last member" per my if statement if ( b == a3ls ).

animations is a large array truncated version looks like:

animations = [
    ['.arrows', 'fadeIn', [1000], [
        ['.heatGenComps', 'fadeIn', [1000] ],
        ['.heatGenComps', 'delay', [2000] ],
        ['.heatGenComps, .arrows', 'fadeOut', [1000] ]
        ]
    ],
    ['.pcb_cad_cfd', 'fadeIn', [1000] , [
        ['.wePredOpTemps', 'fadeIn', [1000] ],
        ['.wePredOpTemps', 'delay', [2000] ],
        ['.wePredOpTemps, .pcb_cad', 'fadeOut', [1000] ]
        ]
    ],
]

nested iteration code:

    //iterate through nested array,
        function iterSub( a, a3ls ){
            b = a[3].shift(); //grab active of nested array
            console.log('a3ls: ' + a3ls);
            console.log('a is: ' + a );
            console.log('b is: ' + b);
            console.log('a[3] is: ' + a[3]);

            if ( b )
            {
                animations.push(b); // add active value back to animations array for infinite loop
                if ( b == a3ls ) //if active is last of array then
                {
                    console.log("last member of b array");
//run animations with promise and done then call top level array iterations
                    $.fn[ b[1] ].apply( $( b[0] ), b[2] ).promise().done( function(){
                        iter();     
                    });

                }
                else //more members left to iterate 
                {
                    console.log("b member");
//run animations and call sub with destructed array and the copy of the last value
                    $.fn[ b[1] ].apply( $( b[0] ), b[2] );
                    iterSub( a, a3ls );
                }

             }
             else //no more elements left
             {
                console.log("b does not exists");
             }
        };

iteration code which calls nested iteration if there is nested array:

    function iter(){

        if (!animating) return;

            a = animations.shift(); //active array

            if (a) //if there is something, do something
            {

                console.log("a exists"); //log a
                animations.push(a); //put a back to the bottom of array for infinite loop

                 if ( a[3] ) //if there is a nested array then
                 {
                    a3ls = a[3][ a[3].length-1 ].slice(); //make a copy of the last element of nested array before shift destructs the array
                    console.log("a[3] exists");
                    $.fn[ a[1] ].apply( $( a[0] ), a[2] ); //applied some jquery animations based on array parameters
                    iterSub( a, a3ls  ); //call function to iterate through nested array and pass it the a array and a copy of the nested array's last value.
                 }
                 else //no nested array then do this
                 {
                    console.log("a[3] does not exist");
//use array to run jquery animations, promise, done, iterate to next 
                    $.fn[ a[1] ].apply( $( a[0] ), a[2] ).promise().done( function(){
                        iter();
                    });
                 }
            }
            else //no a, nothing to do
            {
                return alert('a does not exist');
            }

    };

EDIT when I do if(b.toString == a3ls.toString) the test works prints out "last member of array" even when it's not the last member... think it's because the .toString function is the same.

Answer 1

You have the answer to your question in your own code.

a3ls = a[3][ a[3].length-1 ].slice(); //make a copy of the last element of nested array before shift destructs the array

a3ls is a COPY of the actual element (slice always returns a new array). In itersub , b is the actual element. Javascript == is based on reference. It doesn't actually check whether the two arrays contains the same elements. It only checks whether the two variables point to the same object, which in this case they don't.

You have two options.

• 1. Don't make copy. a3ls = a[3][ a[3].length-1 ]
• 1. Implement some external logic that checks whether each element of b exists in a3ls and vice versa.

You might also have a 3rd option. Don't use shift . Use a simple for loop and check if current index === length - 1 .