javascript - 为什么要用 [].shift.call( array )之类的方法实现array.shift()呢

Question

# 下面这几个函数里面为什么用call() 这种方式呢 

function.prototype.bind = function () {
    var self = this,
    context  = [].shift.call(arguments),
    args     = [].slice.call(arguments);
    
    return function () {
        return self.apply( context, [].concat.call(args, [].slice.call(arguments)) )
    } 
}


var objectFactory = function () {
    var obj = new Object,
    Constructor = [].shift.call( arguments );
    ......
}

var hasProp = {}.hasOwnProperty;
var extends = function ( child, parent ) {
    for(var key in parent) {
        if (hasProp.call( parent, key)) {
            ......
        }
    }
    ......
}