Uncaught TypeError: sum is not a function

<pre name="code" class="javascript"><span style="color: rgb(51, 51, 51); font-size: 13px; line-height: 20.02px; font-family: Arial, Helvetica, sans-serif;">function sum(x,y) </span><span style="color: rgb(51, 51, 51); font-family: Arial, Helvetica, sans-serif; font-size: 13px; line-height: 20.02px;">{</span>

<span style="color: rgb(51, 51, 51); font-family: Arial, Helvetica, sans-serif; font-size: 13px; line-height: 20.02px;">    sum = x + y; </span>

<span style="color: rgb(51, 51, 51); font-family: Arial, Helvetica, sans-serif; font-size: 13px; line-height: 20.02px;">   document.write(sum+"<br/>");</span>

<span style="color: rgb(51, 51, 51); font-family: Arial, Helvetica, sans-serif; font-size: 13px; line-height: 20.02px;">}</span>

<span style="color: rgb(51, 51, 51); font-family: Arial, Helvetica, sans-serif; font-size: 13px; line-height: 20.02px;">sum(1,2);</span>

<span style="color: rgb(51, 51, 51); font-family: Arial, Helvetica, sans-serif; font-size: 13px; line-height: 20.02px;">sum(3,4);</span>

報錯：Uncaught TypeError: sum is not a function

原因：變量和函數同名，導致歧義

改爲:

</pre><pre name="code" class="javascript"><pre name="code" class="javascript">function sum(x,y) {
    all = x + y;
    document.write(all+"<br/>");
}

<pre name="code" class="javascript">sum(1,2);
sum(3,4);