typeof var 显示预期的数字类型后出现意外的 NaN 输出

Question

在 Eloquent Javascript 第 4 章的练习中得到意外的 NaN，但错误不够明显，我无法理解。有人介意看一下并指出我的错误吗？

/*
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 );

这里是 Firebug 输出，显示 func 中 for 循环后的 typeof total 总和确实是 number 但随后输出为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

感谢任何帮助。

Answer 1

问题就在这里

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

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

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 );

Answer 2

这里唯一的错误是你有

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

应该是

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

数组的长度是最后一个索引+1；因此，当在循环的最后一次迭代中使用 <= 时，numRng[i] 将是未定义的，并且将数字添加到未定义会得到 NaN。

typeof var 显示预期的数字类型后出现意外的 NaN 输出

Unexpected NaN output after typeof var displays expected numer type

javascript

nan