Question

在Eloquent Javascript第4章的练习中获得意外的NaN，但错误不足以让我接受它。有人会介意看看我的错误吗？

/*
Write a range function that takes two arguments, start and end, and returns an array containing all the numbers from start up to (and including) end.
*/
var numRng = [];
function range( start, end ) {
  //var numRng = [];
  cntr = ( end - start );
  for ( i = 0; i <= cntr; i++ ) {
    numRng.push( start );
    start++;
  } // end FOR
  //return numRng;
} // end FUNC range

range( 1, 10 );
/*for ( i = 0; i < numRng.length; i++ ) {
  console.log( 'Array element ' + numRng.indexOf( 1 + i ) + ' contains range value: ' + numRng[i] );
}*/

/*
Next, write a sum function that takes an array of numbers and returns the sum of these numbers. Run the previous program and see whether it does indeed return 55.
*/
var total = 0;
function sum( numRng ) {
  //var total = 0;
  for ( i = 0; i <= numRng.length; i++ ) {
    //console.log( total );
    total += numRng[i];
    //console.log( total );      
  } // end FOR
  console.log( typeof total );
  console.log( total );      
} // end FUNC range

sum( numRng );
console.log( 'Total sum of all element values held by array numRng is: ' + total );

这是Firebug输出，在typeof total总和中的for循环确实func之后显示number，然后输出为NaN。

var numRng = []; // seem to require global var ...nt values held by array numRng is: ' + total ); 
number
NaN
Total sum of all element values held by array numRng is: NaN

任何帮助表示感谢。

Answer 1

问题出在这里

for ( i = 0; i <= numRng.length; i++ )
                ^

numRng[numRng.length] =＆gt;未定义
我更正了下面的代码

＆＃13;

var numRng = [];
function range( start, end ) {
  //var numRng = [];
  cntr = ( end - start );
  for ( i = 0; i <= cntr; i++ ) {
    numRng.push( start );
    start++;
  } 
} 

range( 1, 10 );


var total = 0;
function sum( numRng ) {
  for ( i = 0; i < numRng.length; i++ ) {
    total += numRng[i]; 
  }
  console.log( typeof total );
  console.log( total );      
}
sum( numRng );
console.log( 'Total sum of all element values held by array numRng is: ' + total );

＆＃13;

Answer 2

这里唯一的错误是你有

for ( i = 0; i <= numRng.length; i++ )

哪个应该是

for ( i = 0; i < numRng.length; i++ )

数组的长度是最后一个索引+ 1;所以当在循环的最后一次迭代中使用＆lt; =时，numRng [i]将是未定义的，并且向undefined添加一个数字会给你NaN。

typeof var之后的意外NaN输出显示预期的数字类型

2 个答案: