第八章的Flexsum的例子，书上的代码如下：
function flexisum(a) {
var total = 0;
for(var i = 0; i < arguments.length; i++) {
var element = arguments[i];
if (!element) continue; // Ignore null and undefined arguments
// Try to convert the argument to a number n,
// based on its type
var n;
switch(typeof element) {
case "number":
n = element; // No conversion needed here
break;
case "object":
if (element instanceof Array) // Recurse for arrays
n = flexisum.apply(this, element);
else n = element.valueOf(); // valueOf method for other objects
break;
case "function":
n = element(); // Try to invoke functions
break;
case "string":
n = parseFloat(element); // Try to parse strings
break;
case "boolean":
n = NaN; // Can't convert boolean values
break;
}
// If we got a valid number, add it to the total.
if (typeof n == "number" && !isNaN(n)) total += n;
// Otherwise report an error
else throw new Error("sum(): can't convert " + element + " to number");
}
return total;
}
我调试后发现这个apply应用的不太对，应该是call。我将这个例子改进了一下（当然也改动了一下），代码如下：
<html>
<head>
<title>
</title>
</head>
<body>
<script language="javascript">
function flexsum(arr) {
var rst = 0;
if (arr instanceof Array || typeof arr == "object" && "length" in arr) {
for (var i = 0 ; i < arr.length; ++i) {
if (!arr[i]) {
continue;
}
else {
var n;
if (typeof arr[i] == "number") {
n = arr[i];
}
else if (typeof arr[i] == "function") {
n = arr[i]();
}
else if (typeof arr[i] == "string") {
n = parseFloat(arr[i]);
}
else if (typeof arr[i] == "boolean") {
if (arr[i]) {
n = 1.0;
}
else {
n = 0.0;
}
}
else if (typeof arr[i] instanceof Array || typeof arr[i] == "object" && "length" in arr[i]) {
n = flexsum.call(this, arr[i]);
}
else { // typeof arr[i] == "object"
n = arr[i].valueOf();
}
if (typeof n == "number" && !isNaN(n)) {
rst += n;
}
}
}
return rst;
}
else {
throw new Error("The argument " + arr.toString() + "is not a Array or Arraylike object!");
}
}
var arr1 = [1,2,3];
document.write(flexsum(arr1) + "<br>");
var arr2 = [1,2,3,"4", [5,6,7]];
document.write(flexsum(arr2) + "<br>");
</script>
</body>
</html>
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