textContent not working in IE, use innerHTML

My javascript is working fine in FireFox and Safari but when use IE (mine is IE7), it's give me problem [Undefined].

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this.post[i].head = this.posts[i].getElementsByTagName('a')[0];
this.post[i].title = this.post[i].head.textContent;
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Spend hours to check on the issue and finally found a very simple way to solve it, use innerHTML instead of using textContent.

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this.post[i].head = this.posts[i].getElementsByTagName('a')[0];
this.post[i].title = this.post[i].head.innerHTML;
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problem solve.